Revision of the Middle American clade of the ant genus Stenamma Westwood (Hymenoptera, Formicidae, Myrmicinae)

Abstract Stenamma is a cryptic “leaf-litter” ant genus that occurs in mesic forest habitats throughout the Holarctic region, Central America, and part of northwestern South America (Colombia and Ecuador). The genus was thought to be restricted primarily to the temperate zone, but recent collecting efforts have uncovered a large radiation of Neotropical forms, which rival the Holarctic species in terms of morphological and behavioral diversity. By inferring a broad-scale molecular phylogeny of Stenamma, Branstetter (2012) showed that all Neotropical species belong to a diverse Middle American clade (MAC), and that this clade is sister to an almost completely geographically separated Holarctic clade (HOC). Here, the Middle American clade of Stenamma is revised to recognize 40 species, of which 33 are described as new. Included in the revision are a key to species based on the worker caste, and for each species where possible, descriptions and images of workers and queens, images of males, information on geographic distribution, descriptions of intraspecific variation, and notes on natural history. Several species groups are defined, but the majority of species remain unassigned due to a lack of diagnostic morphological character states for most molecular clades. The following species are redescribed: Stenamma alas Longino, Stenamma diversum Mann, Stenamma expolitum Smith, Stenamma felixi Mann, Stenamma huachucanum Smith, Stenamma manni Wheeler, and Stenamma schmidti Menozzi. The following are described as new: Stenamma andersoni sp. n., Stenamma atribellum sp. n., Stenamma brujita sp. n., Stenamma callipygium sp. n., Stenamma catracho sp. n., Stenamma connectum sp. n., Stenamma crypticum sp. n., Stenamma cusuco sp. n., Stenamma excisum sp. n., Stenamma expolitico sp. n., Stenamma hojarasca sp. n., Stenamma ignotum sp. n., Stenamma lagunum sp. n., Stenamma llama sp. n., Stenamma leptospinum sp. n., Stenamma lobinodus sp. n., Stenamma longinoi sp. n., Stenamma maximon sp. n., Stenamma megamanni sp. n., Stenamma monstrosum sp. n., Stenamma muralla sp. n., Stenamma nanozoi sp. n., Stenamma nonotch sp. n., Stenamma ochrocnemis sp. n., Stenamma pelophilum sp. n., Stenamma picopicucha sp. n., Stenamma saenzae sp. n., Stenamma sandinista sp. n., Stenamma stictosomum sp. n., Stenamma tiburon sp. n., Stenamma tico sp. n., Stenamma vexator sp. n., and Stenamma zelum sp. n. Although many of the newly defined species consist of challenging species complexes, this study establishes a robust baseline that will guide future work on the systematics of MAC Stenamma. The total global diversity of Stenamma now includes 84 extant species.

a few aberrant species penetrating into the Neotropics. This view, however, is no longer tenable as increased collecting efforts in the region over the last fifty years, combined with greater use of leaf-litter extraction techniques (e.g. Winkler bags, Berlese funnels), have revealed a trove of new species in Middle America. Together, these new forms rival the Holarctic fauna in terms of morphological, ecological and species-level diversity.
On a global scale, understanding of Stenamma has been greatly improved by several recent studies that incorporate molecular data. First, two investigations looking at higher-level relationships among ants found that Stenamma is closely related to the genera Aphaenogaster Mayr, Messor Forel, Goniomma Emery, and Oxyopomyrmex André (Brady et al. 2006, Moreau et al. 2006). Although not formally described, this clade of genera will likely form a revised version of the tribe Stenammini, which as currently defined is not monophyletic. Next, Branstetter (2009) used molecular and morphological data to redefine Stenamma, providing a new diagnosis of the worker caste, as well as evidence that Stenamma is likely monophyletic. Lastly, and most pertinent to this study, Branstetter (2012) inferred a densely sampled broad-scale phylogeny of Stenamma, revealing that the genus is composed of two, well-supported clades: a "Holarctic clade" (HOC) and a "Middle American clade" (MAC).
The HOC currently consists of 44 extant species distributed across the Nearctic and Palearctic regions, with most Nearctic forms occurring north of Mexico (only a few records from northern Baja California). Species in the MAC occur from the southwestern U.S.A. to northwestern South America (Colombia, Ecuador), with most of the diversity occurring in the wet forests of eastern Mexico and Central America ( Figure 1). The only MAC species to reach the U.S.A. and to co-occur with HOC species is S. huachucanum Smith, which is known from the sky islands of Arizona, New Mexico, and Texas, as well as from many sites in Mexico (Texas record in Van Pelt 1983). Therefore, the two clades are almost completely geographically isolated from one another. Within the MAC, Branstetter (2012) further identified two main clades, a depauperate northern clade, which includes S. excisum sp. n. and S. lagunum sp. n., and the "MAC core," which contains the majority of Neotropical diversity.
I present here the first comprehensive revision of the Middle American clade of Stenamma, recognizing 40 species, of which 33 are described as new. This work represents the first all-in-one treatment of Neotropical taxa since Smith's (1962) review, which included only five species. It is also the first clade-based, rather than regionbased Stenamma revision, taking advantage of the strong phylogenetic framework described above. The focus of this study is on the worker caste, but descriptions of the queen caste, and images of both the queen and male castes are provided when possible. Many of the species described here represent difficult complexes, and in most cases, these are treated as widespread, polytypic species. Although additional data are needed to refine species boundaries within complexes, this study establishes a robust baseline for future work on the systematics of MAC Stenamma.
The first realization that Middle America contained a diverse radiation of previously unknown Stenamma species came from collections made in Costa Rica by J. T. Longino and the Arthropods of La Selva project (ALAS; http://viceroy.eeb.uconn.edu/ALAS/ ALAS.html), which he and R. Colwell organized. Later, it was discovered that several coleopterists (R. S. Anderson, A. F. Newton, S. B. Peck), who used Berlese funnels extensively, had collected many Stenamma specimens as bycatch over the last 50 years from throughout Mexico and Central America. Much of this material was processed at various institutions, but was aggregated at the Los Angeles County Museum (LACM) by the late R. R. Snelling who began to revise Neotropical Stenamma (Snelling pers. comm.). Additional material from the coleopterists was stored in the Field Museum of Natural History (FMNH) bulk sample collection and reviewed by myself. Over the last six years, a very large amount of material has come from the Leaf Litter Arthropods of MesoAmerica project (LLAMA; https://sites.google.com/site/longinollama/), organized by J. T. Longino and R. S. Anderson. This project has intensively sampled leaf litter insects from tropical wet forests in Chiapas, Guatemala, Honduras, and Nicaragua. Many new species were collected by LLAMA, but just as importantly, the project has provided fresh specimens for the molecular studies described above and on-going work. A significant amount of material has come also from personal collections made during LLAMA expeditions.

Overview of natural history
Biological information specific to individual species is provided below in the species accounts. Here I present a summary of what is known about the natural history of MAC one with brood and a queen; they build each nest with a vertical (S. expolitum) or horizontal (S. alas) turret sunk into a shallow alcove; and they maintain a small clay "doorpebble," which is used to block the nest entrance upon encounter with the appropriate disturbance. Reported here for the first time, several other Stenamma species are now known to nest in clay banks. I have found S. diversum Mann, S. megamanni sp. n., S. muralla sp. n., and S. pelophilum sp. n. all nesting in clay banks along streams or on steep clay slopes. Stenamma diversum is particularly interesting, because it has convergently evolved the same nest architecture as S. alas (Branstetter pers. obs.). It nests exclusively in steep clay substrate, and builds a nest entrance with an ear-like turret sunk into the clay. It does not, however, appear to build multiple nests per colony or maintain a door-pebble. Based on where I have collected workers and how the workers are sculptured, I believe other Stenamma species nest in clay banks as well (e.g. S. llama sp. n., S. lobinodus sp. n.). Why does Stenamma nest in clay banks? I hypothesize that like cloud forests, the clay bank habitat is less hospitable to the average ant, and thus provides Stenamma species with a more protected and less competitive environment in which to nest and forage.
Stenamma colonies tend to be small and simple, but there is considerable variation in size and structure. Stenamma diversum, for example, has very small colonies. Nests consist of a single chamber and have at most a dozen workers, a few alates, brood, and a single dealate queen. In contrast, colonies of S. manni and S. megamanni are very large. I have found mature colonies of both species in logs and in the ground (usually underneath a log or rock). They tend to have many chambers containing several hundred to perhaps a thousand workers, along with brood and alates (a thorough census has not been performed). Stenamma alas and S. expolitum have colonies of intermediate size, with up to 200 workers, 50 alates, brood, and a single dealate queen (Longino 2005). Data from nest collections suggest so far that all Stenamma species are monogynous, and that most produce winged queens and males. It is unknown how often alates are released and how far they are able to disperse.

Analysis of morphology
Morphological observations were performed at up to 63x magnification using a Leica MZ12.5 stereomicroscope. Measurements were made with Syncroscopy Auto-Montage software by using the measuring tool (calibrated with a stage micrometer) on single images taken at 70× magnification with a JVC KY-F75U digital camera attached to a Leica MZ16A stereomicroscope. Color montage images were created using the same equipment setup used for measurements, except stacks of images were combined with the program Zerene Stacker (http://zerenesystems.com/cms/home) rather than Auto-Montage. Adobe Photoshop and Illustrator, both CS5, were used to enhance images and create Figures.

Data management
Collection and specimen data for all material examined in this study, along with all color images, have been uploaded to AntWeb (http://www.antweb.org), a site hosted by the California Academy of Sciences. AntWeb subsequently provides all specimenlevel data, images, and natural history content to the Global Biodiversity Information Facility (http://www.GBIF.org), the Encylopedia of Life (http://www.EOL.org), and Wikipedia (http://www.Wikipedia.org). The most important linking fields for specimen data are the collection and specimen codes.
Collection codes link specimens to collection and locality information. They are essentially "lot numbers," meaning they apply to many specimens, and should not be confused with specimen codes. When collections are from individual collectors these codes usually are formed by the collector's initials followed by a number, e.g. MGB1471 for a personal collection. Collections from the ALAS or LLAMA projects have longer codes, in which each part of the code contains information specific to the project, e.g. Wa-B-03-1-32 for a LLAMA collection. All data from the ALAS and LLAMA projects are available from their respective websites (addresses given above). If labels lacked a collection code, then a generic ANTC# code was added to the pin.
Specimen codes, also referred to as "unique specimen identifiers," were attached to all pins examined in this study. It is usually intended that these codes refer to single specimens only, but some pins studied here included multiple mounted specimens. In these cases, rather than add multiple specimen codes to a single pin, or remove specimens from a pin, I treat the specimen code as a pin code and add text following the code to unambiguously identify which specimen is being referenced (e.g. top specimen).
Specimen and collection data were transcribed primarily from an electronic database and therefore may not exactly match label information. All distances and elevations are provided in metric units, converted from feet or miles when necessary. All latitude and longitude coordinates are provided in decimal degrees, with up to five decimal places, depending on the precision of the measurement. In cases where coordinates were not present on a label, these were estimated using Google Earth (http://www.google.com/ earth/index.html), the GEOnet Names Server (http://earth-info.nga.mil/gns/html/ index.html), the FMNH bulk sample database (http://emuweb.fieldmuseum.org/arthropod/bulksamples.php), and/or data already available on AntWeb. Estimated coordinates are indicated with brackets and often include an error estimate on AntWeb. Data  The material examined section of each species account presents an overview of a species distribution (i.e. map data). It is not an exhaustive list of every specimen examined for a particular species. In general it includes one collection from every site where a species has been collected, with each site separated by at least 2km from other sites. In some cases a series of very close records were included to capture elevational range information at a particular site. The format for this section is the same as for type material, except without the [Error], [Habitat], [Microhabitat], [Collection Code], [Repository], or [Specimen Code] fields. Complete data for all examined specimens are available on AntWeb.
Maps for each species were generated using the software ArcGIS v10.1 (Esri, Redlands, CA). The mountainous basemap used in all maps was accessed within ArcMap, but is attributed to the U.S. National Park Service.

Species delimitation
The underlying philosophy driving the separation of species in this study is that of the biological species concept, in which good species represent reproductively isolated entities consisting of one to many populations connected by gene flow (Coyne and Orr 2004). Evidence for reproductive isolation came from finding morphological and/or genetic discontinuities that are maintained in sympatry among closely related forms. The genetic data used here come from Branstetter (2012), as well as from a growing unpublished dataset that includes samples from multiple populations for many of the variable species.
Stenamma taxonomy is complicated by several phenomena. First, species are almost always represented by morphologically distinct, allopatric populations, in which intrapopulation variation is less than interpopulation variation. If one were to split all of these variants into species, there would be two to three times more MAC species than included here. Second, many species show exceptional variation along elevational gradients ( Figure 2). Usually, populations at lower elevations are smaller and more heavily sculptured, while populations at higher elevations increase in size, become darker in color, and have smooth shiny sculpture. If one compares only specimens from low and high elevations they often appear exceptionally divergent, but I have found that it is common for specimens from intervening elevations to have intermediate phenotypes. Consequently, without having thorough geographic coverage, delimiting Stenamma species is a rather arbitrary task. In general, I lump morphological variants into widespread polytypic species if intermediate forms are present and the genetic data are ambiguous, and I split variants into species if they seem "sufficiently" divergent and occur at multiple sites. All species described here should be treated as hypotheses to be tested once more data become available. My reasoning for species delimitation decisions is provided in the comments section of each species account. also varies in orientation, usually projecting anteriorly, but sometimes projecting more ventrally, making it difficult to view.
The structure of the basal margin of the mandible usually correlates with the shape of the anterior clypeal margin (see Figure 19). This is because clypeal teeth, if present, usually merge with the basal margin of the mandible when the mandibles are closed. When the anterior clypeal margin is entire or only has a median emargination, the basal margin of the mandible is straight to slightly sinuous. When the anterior clypeal margin is undulating or forming teeth, the basal margin of the mandible is sinuous and usually has a distinct, shallow to deep basal depression. In some species, the basal depression is accompanied by a small tooth that projects inward from the proximal edge of the depression.
The clypeus and basal margin of the mandible are very useful in species identification. Consequently, it is highly recommended that specimens be mounted with mandibles open. If all specimens from a series have the mandibles closed, then the mandibles should be carefully pried open (before mounting) by pushing a pin between the mandibles from the ventral side of the head.
Color. Overall body and appendage color and the contrast between the two can be very useful in separating some species. Body color ranges from jet black to pale yellow, with red-black, brown-black, orange-brown, or brown as common intermediate colors. Sometimes species have a mottled appearance, with areas of dark or light cuticle occurring irregularly. Appendages are almost always lighter in color, usually becoming very light toward the extremities. It is important to note that older museum specimens lose their color, often having a faded red-brown color (see Figures 73,82,85,150).
Gastral pilosity. On a given Stenamma specimen, pilosity on the body dorsum is generally similar in form, but it is usually best viewed on the gastral tergites. Among species, pilosity varies in length, density, thickness, and whether or not it is separated into two distinct layers ( Figure 5). There is a continuum from being long, sparse, and clearly single layered, to being short, dense, and clearly bilayered, with the bilayered pilosity consisting of a longer layer of suberect to subdecumbent setae and a shorter layer of subdecumbent to appressed setae. The suberect, upper layer of setae can sometimes be distinctly thickened (i.e. stout), and the lower layer can be either very sparse or very dense and thin, becoming pubescent. Using this character is complicated by the fact that some species have intermediate character states and some species show substantial intraspecific variation.
Sculpture. In principal I adhere to the terminology and philosophy of Harris (1979). Surface sculpture varies greatly among MAC Stenamma species and is a very good separatory character. There are three main patterns of sculpturing: entire body smooth and shiny; face smooth and shiny, but mesosoma mostly sculptured; and head and mesosoma completely sculptured. It is also common for the pronotum to become smooth and shiny, whereas the remainder of the body is sculptured ( Figure 6). The gaster is usually always smooth and shiny except for a few species that have variably developed basal punctae. Sculpture types include carinae, rugae, rugoreticulae, costae, punctae, and foveae, as well as the diminutive forms of all types. I often use the term punctae in a broad sense to refer to what might also be described as punctulae or foveolae. Species that occur over a broad elevational range usually have variable sculpturing, with specimens from higher elevations becoming smoother and shinier. Species that vary substantially in this way are more difficult to characterize.
Frontal lobes and posterior extension of the clypeus. There is significant variation in the width of the frontal lobes and the width of the depressed area in between the lobes (Figure 7). In some species the frontal lobes are strongly expanded laterally or dorsolaterally. This variation is characterized quantitatively with the measurement FLD and the index FLI. It is also described qualitatively by whether or not the underlying torular lobes are covered by the frontal lobes in full-face view. The area in between the frontal lobes, referred to here as the posterior extension of the clypeus, can be very narrow to quite wide, with the sides varying in shape from subparallel to strongly hour- glass shaped. An attempt to quantify this variation is made with the measurement PCW. Both of these characters are useful, but most species display intermediate values.
Petiole and postpetiole shape. Many Stenamma species have very distinctive petiole and postpetiole shapes ( Figure 8). Categories of qualitative descriptors include overall robustness, symmetry of the nodes (in profile), and sharpness and angle of node apices. I also attempt to capture variation quantitatively with length, width, and height measurements of each segment. Often these are most useful as ratios. For example, if the postpetiole is very wide in relation to the petiolar node, I include an index such as PPW/ PW. The actual index used depends on the distinctive feature for a particular species.
Promesonotum shape. The shape of the promesonotum in profile is variable and can be very distinctive in some species (Figure 9). The average form is for it to be low-domed and roughly symmetrical from front to back, but it can become distinctly asymmetrical, with the apex shifted away from the midpoint, or with the anterior or posterior slope much longer than the other. It can also be distinctly bulging, becoming high-domed.  Propodeal spines. The propodeal spines in Stenamma can be absent to quite long and robust ( Figure 9). To quantify this character I use the measurement PSL and the index PSI. I also describe them as absent, tuberculate, short, medium, or long. When absent, the juncture of the propodeal dorsum and declivity can be smoothly rounded or it can form a sharp angle.

Discussion of Middle American clade (MAC)
The MAC is distributed from the southwestern U. S.A. (Arizona, New Mexico, Texas) to northwestern South America (Colombia, Ecuador) ( Figure 1). It is known to cooccur with the Holarctic clade only in the southwestern U.S.A, where S. huachucanum reaches the northern limit of its range. In this area of sympatry it is easy to separate the two clades based on the structure of the anterior clypeal margin and basal margin of the mandible (Branstetter 2012). In S. huachucanum the anterior clypeal margin forms four teeth, and the basal margin of the mandible is sinuous and has a slight basal depression. In contrast, the HOC species have the anterior clypeal margin with a simple median  emargination (can be difficult to see in impar group species) and the basal margin of the mandible straight. The HOC species also tend to have very conspicuous longitudinal clypeal carinulae, whereas these are reduced in S. huachucanum and most MAC species.
Using just the worker caste it has not been possible to find diagnostic features that adequately distinguish the MAC from the HOC. In general, MAC species exhibit a much greater diversity of phenotypes, resulting in an abundance of autapomorphies. The following features help define the MAC: clypeal carinae usually faint or absent (usually more distinct in HOC); structure of the anterior clypeal margin more variable than in HOC, often forming distinct teeth (usually a simple median emargination in HOC); structure of the basal margin of the mandible more variable, often sinuous, with a distinct basal depression or notch (usually straight in HOC); surface sculpture often reduced, sometimes completely smooth and shiny (HOC species usually completely sculptured); form of pilosity on gastral dorsum more diverse (HOC species usually with pilosity short, bilayered, and not noticeably thickened); gastral tergites and sternites usually smooth and shiny (only sometimes punctate in S. huachucanum and S. manni, and with short basal carinulae in S. atribellum sp. n. and S. callipygium; HOC species commonly with basal carinulae and punctae).
A global diagnosis of the worker caste of Stenamma is presented in Branstetter (2009), with some additional notes comparing MAC and HOC Stenamma species. Within the Neotropics, Stenamma is likely to be confused only with the myrmicine genera Adelomyrmex Emery, Aphaenogaster Mayr, Lachnomyrmex Wheeler, Megalomyrmex Forel, Pheidole Westwood, or Rogeria Emery. Stenamma can be separated from these genera by having the following combination of characters: antenna 12-segmented; flagellum with a distinct to indistinct 4-segmented club; propodeum in profile depressed compared to promesonotum; posterior extension of the clypeus between antennal insertions relatively narrow and long (only broad in a few species).

Discussion of species groups
Using worker morphology and results from molecular phylogenetic analysis (Branstetter 2012, unpublished data), an attempt was made to create morphologically diagnosable, monophyletic species groups within MAC Stenamma. However, for most well-supported clades within the MAC, this was not possible due to significant morphological variability and homoplasy among species. The few exceptions to this are the following: (I) atribellum group (S. atribellum, S. callipygium), (II) diversum group (S. diversum, S. tico sp. n.), (III) expolitum group (S. alas, S. expolitico sp. n., S. expolitum), and (IV) lobinodus group (S. llama, S. lobinodus, S. tiburon sp. n.). If species complexes become better resolved and the reproductive castes are studied in more detail, additional species groups may be identified. To simplify the organization of this revision, the species accounts below are ordered alphabetically by species, rather than by species group. Diagnostic character states for each group can be found in the key and in the individual species accounts.
Medium-to large-sized species; general body color black to dark red-brown, with appendages uniformly orange-brown (type population), or mostly dark brown changing to orange-brown at joints and extremities; setae golden brown; mandible with 5-7 teeth, consisting of 4 distinct apical teeth, a basal tooth, and 1-2 worn teeth/denticles in between; basal margin of mandible straight, without a basal notch or depression; mandible surface mostly smooth, with scattered piligerous punctae and a few striations on base and lateral surface; anterior clypeal margin with a median emargination; median lobe of cl-ypeus obliquely flattened, mostly smooth and shiny, with a short transverse carinula near anterior margin, remainder of clyepeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions somewhat wide (PCW 0.05-0.09), with sides sub- parallel to slightly diverging anteriorly; frontal lobes of moderate width , not greatly obscuring torular lobes in full-face view; head roughly ovalshaped , with posterior margin flat, to genetly convex, not depressed medially; eye relatively large (EL 0. , oval-shaped, with 8-10 ommatidia at greatest diameter; face with a fan of carinulae extending from frontal lobes to just past midpoint of head (type population) or further, sometimes reaching posterior and lateral margins, carinulae when completely covering face, often very dense (almost striate); gena with some carinulae; posterolateral and ventral surfaces of head smooth and shiny; scape of moderate length (SI 83-101), reaching, but not distinctly surpassing posterior margin of head in full-face view; scape surface mostly smooth, with scattered piligerous punctae; flagellum with distinct 4-segmented antennal club; promesonotum completely smooth and shiny (type population), or with a variable number of transverse striae on dorsal surface, remainder of mesosoma mostly smooth, except for transverse carinulae on propodeal dorsum, and a few rugulae on side of propodeum and mesopleuron; promesonotum in profile domed, symmetrical, and moderately to strongly bulging; metanotal groove distinct, but often shallow; propodeal spines absent (PSL 0.10-0.15, PSI 0.7-1.0); dorsum of propodeum in profile slightly to strongly convex, usually not flat; petiole and postpetiole almost completely smooth and shiny, with only faint vestigial punctae sometimes present, mostly on venters; postpetiole in profile bulging, globular, appearing more voluminous than petiolar node (PPH/PH 0.89-1.06, PW/PPW 0.73-0.84); petiole in profile appearing of moderate length (PL/HW 0.50-0.58); petiolar node in profile nearly symmetrical, dorsum of node broadly rounded, and pointed vertically to slightly posteriad; gaster smooth and shiny, with scattered piligerous punctae; face with short suberect to decumbent pilosity; setae on remainder of body dorsum sparse, long, and mostly suberect; setae on scapes subdecumbent; setae on legs mostly subdecumbent, with longer suberect setae on femoral venters and coxae.
Male. See Figure 49E-G. Biology. The nesting biology of S. alas is described in detail in Longino (2005) and was reviewed in the overview of natural history section above, but is summarized again here. Stenamma alas is a specialized inhabitant of clay bank environments. Nests are found in nearly vertical clay banks along streams or vertical cuts along trails. Stenamma alas occurs in relatively pristine wet forest habitats from 50 to approximately 1800 m (note the holotype form of S. alas only reaches about 1600 m). I have noticed that S. alas is most abundant at mid-elevations between 300-800 m elevation. At lower elevations, S. expolitum, which is a closely related and often sympatric species, seems to be more dominant.
Colonies include one to five closely spaced nests, but the queen, brood, and most of the workers only occupy one of them. Colonies seem to be continually building new nests and occasionally migrating from one to another. Each nest consists of a horizontally oriented ear-like turret that is sunk into a small alcove. The nest entrance is in the middle of the turret. Next to the entrance the workers always maintain a small clay "door pebble" and when the proper stimulus is applied to the nest entrance, such as an army ant or other predaceous ant, an S. alas worker quickly emerges from the nest and closes the entrance with the pebble. It is hypothesized that all of these complex nesting behaviors evolved to avoid predation by army ants. Each S. alas nest contains a single small chamber. Colonies are fairly large for Stenamma, with up to 250 individuals. All excavated colonies have contained only one egg-laying queen. Foragers are solitary, slow moving and freeze when disturbed. It is unknown what S. alas forages on primarily, but I have observed workers returning to the nest with cookie baits and small pieces of unidentified organic matter, suggesting that the species might be a generalist scavenger.
Comments. Stenamma alas, along with S. expolitico and S. expolitum, belongs to the expolitum species group (a diagnosis of this group is given under S. expolitum below). Stenamma alas is easily separated from S. expolitico and S. expolitum by comparing the sculpturing on the face and promesonotal dorsum. In the field, the holotype form of S. alas (discussed below) can be separated from S. expolitum by the structure  of the nest entrance. Stenamma alas nests always have a horizontal turret, whereas S. expolitum nests have vertical turrets.
As I have circumscribed it here, S. alas represents a complex of species, whose boundaries are not clear. The type form of S. alas ( Figure 47) occurs only in Costa Rica. It is characterized by the following: facial carinulae extending to about midpoint of head, but not further; pronotum completely smooth and shiny; legs uniformly orange-brown. Variant 1 ( Figure 48A-C) differs from the holotype form as follows: facial carinulae more extensive, sometimes very dense and extending all the way to the posterior margin of the head; legs dark brown to brown; dorsum of promesonotum with variably developed transverse striations. Variant 2 ( Figure 48D-F) is the same as variant 1 except that the promesonotum in profile is strongly bulging upward, appearing high-domed. Variant 2 is known only from a few localities in the Bocas del Toro and Chiriquí provinces of Panama. It does not occur in sympatry with the other forms and some specimens appear intermediate, with the promesonotum less bulging. There is also variation in how dense and long the facial carinulae appear.
Variant 1 includes specimens from Costa Rica to Ecuador, but it does not appear to be a monophyletic entity. The specimens in Costa Rica occur at high elevation, above 1500 m and Longino (pers. comm.) reported finding nests in the ground, rather than in clay banks. One nest was found in a small clay hummock in the middle of a trail in forest. The other was in the ground under leaf litter in forest. There is some variation in how dense the facial carinulae are among sites, with a specimen from Las Alturas having very dense carinulae, similar to variant 2. The variant 1 specimens in Ecuador look nearly identical to those in Costa Rica, with some variation in facial sculpture. They are from lower elevation (800-900 m) and have nests in clay banks like the type form of S. alas (Donoso, pers. comm.).
Molecular phylogenetic data show that variant 1 specimens from Costa Rica form a clade sister to S. expolitum and S. expolitico (Branstetter unpublished data). Specimens from Ecuador form a clade sister to S. alas. No specimens from Panama have been sampled yet. This result suggests that the variant 1 specimens in Costa Rica are distinct from the type form of S. alas and the specimens in Ecuador, but I cannot tell them apart based on worker or queen morphology. Thus, I treat S. alas as a paraphyletic species, but acknowledge that it could include multiple cryptic taxa. More morphological and molecular data will be needed to resolve this problematic species.  Fortuna-Chiriquí Grande Rd., 8.78333°N, 82.1833°W, 800m, 16 Jul 1987Sendero Divisa, 15km SSW Chiriquí Grande, 8.783°N, 82.200°W, 1250m, 9 Jul 1987  Worker diagnosis. Integument brown to red-brown (note that observed specimens are old, fresh specimens probably darker); small-sized species (see HL, ML, PrW below); anterior clypeal margin undulating, forming 2-4 small blunt teeth; basal margin of mandible sinuous, with a shallow basal depression, but without a basal tooth; head and pronotum mostly smooth and shiny; promesonotum in profile with relatively sharp transitions between anterior and dorsal faces, and between pronotum and mesonotum; pilosity on gastral tergites forming a layer of stout suberect setae, and a sparse layer of decumbent setae; eye of moderate size (EL 0.08-0.09, PSL 0.08-0.10), oval-shaped, with 5 ommatidia at greatest diameter; propodeal spines tuberculate (PSL 0.08-0.10, PSI 1.2-1.3); frontal lobes of moderate width , not obscuring torular lobes in full-face view. Similar species: Stenamma connectum, S. crypticum, S. huachucanum, S. (68), .
Small-sized species; general body color brown to red-brown (note observed specimens are older, fresh material almost certainly darker), with appendages lighter, brown to yellow-brown at extremities; setae golden; mandible with 6 teeth; basal margin of mandible sinuous, with a shallow basal depression, but no basal tooth; mandible mostly smooth, except for some conspicuous basal striae, and scattered piligerous punctae; anterior clypeal margin undulating, forming 2-4 small blunt teeth; median lobe of clypeus smooth, without noticeable carinulae, apex of lobe with a short transverse carinulae, remainder of clypeus smooth and shiny; posterior extension of clypeus between antennal insertions somewhat narrow (PCW 0.03), with sides subparallel; frontal lobes of moderate width , not obscuring torular lobes in fullface view; head roughly oval-shaped (CI 85-88), posterior margin with a slight median depression; eye of moderate size (EL 0.08-0.09, REL 16-17), oval-shaped, with 5 ommatidia at greatest diameter; face almost completely smooth and shiny, except for a few carinulae around frontal lobes and on genae, and scattered piligerous punctae; scape of moderate length (SI 95-98), not quite reaching posterior margin when laid back; scape surface mostly smooth, with faint striations, and scattered piligerous punctae; flagellum with a distinct 4-segmented antennal club; all of pronotum and most of mesonotal dorsum smooth and shiny, anepisternum rugose, katepisternum punctate, side of propodeum mostly punctate, with a few rugulae, dorsum and declivity of propodeum with transverse carinulae; promesonotum in profile low-domed, roughly symmetrical, with relatively sharp (and distinctive) transitions between anterior and dorsal faces, and between pronotum and mesonotum; metanotal groove of well-demarcated, of moderate width and depth; propodeal spines tuberculate (PSL 0.08-0.10, PSI 1.2-1.3); petiole appearing of moderate length (PL/HW 0.53-0.54); petiolar node in profile of moderate height (PH/PL 0.60-0.65), roughly symmetrical, with anterior and posterior faces almost equal in length, node dorsum rounded, but somewhat narrow, pointing vertically; postpetiole in profile subspherical, slightly smaller than petiolar node (PPH/PH 0.84-0.86); petiole and postpetiole mostly lightly punctate, with anterior faces of nodes smooth; gaster mostly smooth and shiny, with scattered piligerous punctae; most of body dorsum with thickened standing pilosity; pilosity on gastral tergites forming a layer of stout suberect setae, and a sparse layer of decumbent setae; setae on scapes dense, decumbent to appressed; setae on legs mostly appressed, with a few suberect to subdecumbent setae on femoral venters and coxae.

Male. Unknown.
Biology. This species is recorded from a single Berlese sample of sifted leaf litter collected in cloud forest at 990 m elevation.
Comments. Stenamma andersoni should be easy to separate from similar species by its smooth head and pronotum, unique pronotum shape, and thickened gastral setae.
Stenamma andersoni is known from only two specimens collected in 1987. As a result the specimens are somewhat faded in color and were not useable for molecular phylogenetic work. With morphology alone, it is not clear to which species S. andersoni is most closely related, but I hypothesize that it is probably near S. crypticum or S. huachucanum.
Medium-to large-sized species; general body color mostly black, with patches of dark brown; appendages black to orange-brown, lighter at extremities; setae dark brown; mandible with 6 teeth, but two teeth nearest basal tooth usually worn and indistinct; basal margin of mandible straight, without basal notch or deep depression; mandible mostly smooth and shining, with scattered piligerous punctae; anterior clypeal margin with a median emargination; median lobe of clypeus smooth and shiny, lacking carinae, remainder of clypeus smooth and shiny; posterior extension of clypeus between antennal insertions of moderate to wide width (PCW 0.04-0.06), sides slightly hourglass-shaped; frontal lobes of moderate width , not obscuring torular lobes in full-face view; head roughly oval-shaped, distinctly longer than broad (CI 87-92), with posterior margin slightly depressed medially; eye relatively large , roughly ovalshaped, with 9-10 ommatidia at greatest diameter; head almost completely smooth and shiny, with short faint longitudinal carinulae around midline of face near antennal lobes; scape relatively long (SI 94-101), just reaching posterior margin of head when laid back; scape surface smooth and shiny, except for scattered piligerous punctae; funiculus with a somewhat distinct antennal club; mesosoma almost completely smooth and shining, except for shallow furrows along metanotal grove, and scattered piligerous punctae; promesonotum in profile low-domed and asymmetrical, with the apex slightly anterior of midpoint; metanotal grove shallow, but distinct; propodeal spines reduced to small tubercles (PSL 0.10-0.13, PSI 0.9-1.0); petiole of moderate length (PL 0.43-0.47, PL/HW 0.52-0.57); petiolar node in profile nearly symmetrical, and of moderate height (PH/PL 0.57-0.60), dorsum smoothly rounded; postpetiole bulging and distinctly wider than petiole (PW/PPW 0.72-0.78), anterior face long and shield-like, posterior face short and truncate; petiole and postpetiole almost completely smooth and shining, with some faint punctae confined mostly to the ventral surfaces; gaster with an elongate anterior constriction and with faint dorsal striae, remainder of gaster smooth and shiny, except for piligerous punctae; most of body dorsum with a layer of moderately long and stout standing pilosity; scape with suberect to decumbent setae; gaster with a layer of suberect setae, and a very sparse layer of short decumbent setae; legs with mostly appressed setae, but some suberect setae on coxae and femoral venters.
Queen Same as worker except for standard queen modifications and as follows: face with a few distinct carinulae extending from frontal lobes to ocelli; mesoscutum, near posterior margin, and scutellum, with some longitudinal carinulae/rugulae.

Male. Unknown.
Biology. This species is a cloud forest specialist ranging from 1550-2030 m elevation, and is known from one leaf litter sample and one nest collection. The nest was collected underneath the bark of a large log in cloud forest near the edge of dwarf forest. The entire nest was not censused, but it was relatively large, with at least 100 workers, a single queen and brood.
Comments. Stenamma atribellum is a distinctive species that should not be confused with any other MAC species. Molecular phylogenetic data show that it is sister to S. callipygium, which is the only other Stenamma species to have an elongate anterior gastral constriction (Branstetter unpublished data). This character joins S. atribellum and S. callipygium in the atribellum species group. Stenamma atribellum can be separated from S. callipygium by its completely smooth and shiny sculpture and emarginate anterior clypeal margin. Furthermore, these species have not been collected in sympatry and both appear to be narrow endemics.
Stenamma atribellum might be confused with the superficially similar S. alas and S. expolitum, which are both mostly smooth and shiny. However, these latter species do not have the anterior constriction of the gaster elongate and they tend to have more facial sculpture (especially in S. alas). These species are also geographically separated from each another.    rugoreticulate; eye relatively small , circular, and slightly bulging, with 5-7 ommatidia at greatest diameter; pilosity on gastral dorsum long, dense and mostly suberect; propodeal spines tuberculate to long and robust, usually of moderate length (PSL 0.15-0.37, PSI 1.3-2.9); anterior clypeal margin forming a single shallow to deep median emargination, or rarely, 4 blunt teeth; basal margin of mandible straight to sinuous, sometimes with a broad basal depression, but without a distinct notch or tooth; 4-segmented antennal club indistinct. Similar species: Stenamma zelum.
Geographic range. Mexico (Atlantic slope) to Honduras. Worker description. Medium to large-sized species; general body color usually red-black (type population) to black, with patches of brown, but some populations more uniformly brown; mandibles and appendages always lighter than body, brown to orange-brown; setae golden brown; mandible with 4-8 teeth (usually 7), consisting of 3-4 distinct apical teeth, a basal tooth, and a variable number of inner teeth, which are often worn and indistinct; basal tooth usually of moderate size (type population), but sometimes more robust and projecting; basal margin of mandible straight to slightly sinuous, sometimes with a shallow, broad basal depression, but without a distinct notch or tooth; mandible mostly smooth and shining, with scattered piligerous punctae and a few lateral striae; median lobe of clypeus usually slightly produced and clearly visible in full-face view (type population), but sometimes becoming obliquely flattened and angled more dorsoventrally, making it less visible; anterior clypeal margin varying from having a shallow to deep median emargination (type population), to forming 4 distinct blunt teeth; median lobe usually with a pair of faint longitudinal carinulae that diverge toward anterior margin, apex of lobe with a faint to strong transverse carinula; posterior extension of clypeus between frontal lobes of relatively moderate width (PCW 0.04-0.07), with sides subparallel to hour-glass-shaped; frontal lobes average to slightly expanded outward , with underlying torular lobes always visible in full-face view; head in full-face view roughly oval shaped to subcircular (CI 85-97), with posterior margin slightly to distinctly depressed medially; eyes relatively small , circular, and somewhat bulging, with 5-7 ommatidia at greatest diameter; head foveate to coarsely rugoreticulate, shiny, often with a few short costae extending back from frontal lobes, interstices with piligerous punctae; scape relatively short, not reaching posterior margin of head when laid back (SI 85-99); scape shiny, usually with only scattered piligerous punctae (type population), but sometimes more robust, with punctae deeper and broader, becoming foveolae; flagellum with indistinct 4-segmented antennal club; mesosoma robust, foveate to coarsely rugoreticulate, with foveae most prominent on promesonotal dorsum; propodeal spines varying from short tubercles to long robust spines (PSL 0.15-0.37, PSI 1.3-2.9), which are usually spiniform and project dorsoposteriorly (type population), but sometimes form robust vertical pointing triangles; promesonotum in profile varying from being domed and nearly symmetrical (type population), to domed and asymmetrical, with apex occurring anterior of midpoint, to high-domed and asymmetrical; humeral angles rounded and indistinct, to becoming produced and angulate (type population), the latter occurring when the promesonotal side is scalloped slightly inward; metanotal grove present, but variable in depth and degree of distinctness; anterodorsal margin of propodeum in profile flat to distinctly raised into a welt (type population); propodeal declivity with a variable number of transverse carinae, often mostly smooth and shiny; petiole shape in profile usually appearing relatively long and somewhat gracile (PL/HW 0.53-0.63), with a small distinct node (PH/PL 0.45-0.55) (type population), but sometimes petiole is more robust and strongly wedge-shaped, without a clear distinction between the node and peduncle; postpetiole in profile usually low-domed, nearly symmetrical, and appearing as high or slightly smaller than petiolar node (type population), but sometimes postpetiole distinctly larger than petiolar node; postpetiole in dorsal view elongate, and reaching its widest point near pos-terior margin; waist sculpture variable, nodes usually mostly smooth and shiny, but sometimes more punctate and/or with longitudinal costae or rugulae, ventral surface punctate, dorsal surface of peduncle punctate and with a variable number of rugulae; gaster mostly smooth and shiny, with scattered piligerous punctae, and short furrows on anterior constriction where gaster inserts into postpetiole; most of body with relatively long standing pilosity; scape either with a single layer of mostly decumbent setae, or bilayered with a sparse layer of longer suberect setae over a denser decumbent layer (type population); gastral pilosity relatively long and somewhat dense, with most setae suberect to subdecumbent; setae on legs suberect to decumbent, with some populations having predominately suberect setae (type population) and others mainly decumbent setae, longer suberect setae always present on femoral venters and coxae.  (97), , , FLI 28-31 (29), PSI 1.1-2.1 (2.1), MFI 87-95 (93), ACI1 63-64 (63), ACI2 80-85 (80).
Same as worker except for standard queen modifications and the following: Propodeal spines less variable (PSL 0.18-0.28, PSI 1.1-2.1), usually present, of moderate length, and thick at base (only Nahá population with spines tuberculate); setae on scape less variable, usually with a sparse layer of longer suberect setae and a layer of denser decumbent setae (only Nahá population with setae uniformly subdecumbent); wing venation as in Figure 56D.
Male. Unknown. Biology. Stenamma brujita is known only from Winkler and Berlese samples of leaf litter collected from the floor of wet forest habitats (e.g. lowland rainforest, montane wet forest, cloud forest, pine cloud forest, oak-pine forest). The species has a broad elevational range, occurring from 200-1800 m, but it is most common at midelevations (1000-1500 m).
Comments. The combination of large size, small eyes, and foveate sculpture make S. brujita a very distinctive species, unlikely to be confused with any other MAC species. However, S. zelum, which is not closely related to S. brujita (Branstetter 2012), has converged on a similar phenotype and may cause problems with identification. Fortunately, these two species are geographically isolated from one another, with S. brujita reaching only as far south as northwestern Honduras, and S. zelum extending only as far north as northeastern Honduras. Using morphology, Stenamma brujita can be distinguished from S. zelum by its more rounded head (rectangular in S. zelum), longer propodeal spines (PSI 1.3-2.9 vs. 1.0-1.3), and lower FLI (27-31 vs. 31-34). In addition, the anterior clypeal margin forms four sharp teeth in S. zelum, with the outer teeth usually strongly projecting. In contrast, most populations of S. brujita have the anterior clypeal margin forming a single median emargination (all Honduras populations like this), and in those specimens that do have clypeal teeth, the teeth are all blunt.
Stenamma brujita is quite variable throughout its range and may comprise a complex of several species. I choose to identify a single species here, because every population exhibits some amount of variation, none of the variants occur in sympatry, and some populations have intermediate phenotypes. I do however, identify three main variants that differ significantly from the holotype population.
Variant 1 ( Figure 54A-C) includes all collections from Tamaulipas and Hidalgo, Mexico. It has the following features: body sculpture more rugoreticulate than foveate; propodeal spines long, straight and more slender; petiole with a distinct concavity below node.
Variant 2 ( Figure 55D-F), the most distinctive variant, is known from a few collections taken on the wet Atlantic slope of the Sierra Juarez, between Oaxaca and Valle Nacional in Mexico. It has the following features: body very large; general body color very dark, mostly black; petiole wedge-shaped, usually without a distinct node; propodeal spines forming robust, blunt-tipped triangles, which point almost vertically.
Variant 3 ( Figure 56G-I) occurs at several localities in Chiapas, México, mainly Nahá and Lago Metzabok. It is characterized by the following: general body color brown; promesonotum in profile high-domed, and asymmetrical; propodeal spines tu-berculate; petiole in profile appearing more gracile with node reduced in size; anterior clypeal margin forming 4 blunt teeth.
Some additional populations in Chiapas, Mexico, and all of the populations in Guatemala and Honduras, are most similar to the holotype population (La Unión, Guatemala). However, there is considerable variation among populations and some have character states that are intermediate between the holotype form and the different variants just described. Specimens from higher elevations tend to be larger, darker and more robust. The specimens from Purulhá, Guatemala appear especially robust-looking, with very long, sinuous propodeal spines and coarser sculpturing. Interestingly, these specimens have the petiolar node more wedge-shaped, similar to variant 2. Key character states of the holotype population are indicated in the worker description.
Material   Worker diagnosis. Integument mostly black; medium-sized species (see HL, ML, PrW below); gaster with an elongate anterior constriction, with anterolateral margins of gaster forming hard shoulder-like angles (best viewed dorsally); median lobe of the clypeus projecting out over mandibles, forming a well-defined, blunt apex; basal margin of mandible sinuous, but without a basal notch or deep depression; basal third of mandible distinctly attenuated (dorsoventrally thinned); face with dense fan of carinulae extending to posterior and lateral margins of head; eye large (EL 0. , oval-shaped, with 9-10 ommatidia at greatest diameter; propodeal spines tuberculate (PSL 0.08-0.10, PSI 1.0-1.4); setae on gastral tergites moderately long and sparse, mostly suberect; frontal lobes of moderate width , not covering torular lobes in full-face view. Similar species: Stenamma atribellum.
Geographic range. Guatemala. Medium-sized species; general body color black to dark brown, with appendages brown to orange-brown; setae dark brown; mandible with 6-7 teeth, consisting of 3-4 distinct apical teeth, an indistinct basal tooth, and 2-3 inner denticles; basal third of mandible distinctly attenuated (dorsoventrally thinned), with masticatory and basal margins somewhat elongated, attenuated section bordered by an oblique carina; basal margin of mandible sinuous, but without a basal notch or distinct depression; mandible surface mostly smooth and shiny, with scattered piligerous punctae; anterior clypeal margin reduced and mostly hidden underneath the median lobe; median lobe of clypeus projecting out over mandibles, forming a well-defined, blunt apex (almost tooth-like), clypeal carinae absent, remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions of moderate to wide width (PCW 0.03-0.06), sides subparallel; frontal lobes of moderate width , but not completely obscuring torular lobes in full-face view; head usually robust and somewhat heart-shaped (CI 86-97), with posterior margin broadly depressed medially; eye large (EL 0.14-0.19, REL20-24), oval-shaped, with 9-10 ommatidia at greatest diameter; face densely sculptured with a fan of longitudinal carinulae that extend to the posterior and lateral margins, area between eye and antennal insertion with shorter irregular rugulae, interstices near lateral margins faintly punctate; scape of moderate length (SI 86-98), just reaching posterior margin of head when laid back; scape surface mostly smooth and shiny, with scattered piligerous punctae and a few striations; flagellum with somewhat distinct 4-segmented antennal club; side and anterior half of pronotum mostly smooth and shiny, with a few scattered rugulae; remainder of promesonotal dorsum longitudinally carinate; mesopleuron and side of propodeum with scattered rugulae and faint punctae; propodeal dorsum and declivity with transverse carinae; promesonotum in profile low-domed and somewhat asymmetrical, with apex occurring anterior of midpoint and the anterior slope longer and steeper than posterior slope; metanotal grove present, somewhat shallow; propodeal spines forming small, but sharp tubercles (PSL 0.08-0.10, PSI 1.0-1.4); petiole of moderate length and form (PL/HW 0.44-0.51); petiolar node in profile somewhat small (PH/PL 0.61-0.67), gently rounded to subquadrate, and slightly angled posteriad, anterior slope distinctly longer than posterior slope; postpetiole bulging, distinctly wider than petiole (PW/PPW 0.60-0.71), and anterior gastral constriction (most noticeable in dorsal view), anterior face of node in profile long and shield-like, posterior face truncate; anterior faces of petiolar and postpetiolar nodes smooth and shiny, posterior faces with a few rugulae and punctae; ventral surface of waist segments faintly punctate; anterior constriction of gaster distinctly elongate and with elongate dorsal striae; gaster in dorsal view with shoulder-like anterolateral corners where anterior constriction begins; remainder of gaster mostly smooth and shiny, with scattered piligerous punctae; most of body dorsum with long standing pilosity; setae on scape subdecumbent to appressed, of roughly uniform length; gastral pilosity somewhat stout and mostly forming a sparse layer of suberect to subdecumbent setae; setae on legs mostly decumbent to appressed, with suberect setae on coxae and femoral venters. Same as worker except for standard queen modifications and as follows: mesosoma almost completely carinulate, only mesopleuron mostly smooth; pronotum with transverse carinulae; pronotum with transverse carinulae that wrap around entire surface; mesoscutum and scutellum with longitudinal carinae; anterior of mesoscutum with a short narrow strip of smooth surface from which carinulae arise; gastral setae slightly more dense.
Male. Unknown. Biology. Stenamma callipygium has been collected by sifting leaf litter, beating vegetation and baiting with cookie bait. In addition, a single worker was found in a flight intercept trap placed underneath a Malaise trap. This species is a cloud forest specialist known from 1630-1750 m elevation. Very few Stenamma species are known from beating samples, suggesting that this species may nest or at least forage arboreally. The diversity of collecting methods that have retrieved this species suggests that it is an active forager. It is surprising, however, that out of the over 100 leaf litter samples collected at the Biotopo Quetzal by the LLAMA project, only one sample had S. callipygium.
The oddly shaped clypeus and mandible of this species is unique within Stenamma and begs for explanation. Most likely the projecting clypeal tooth is used for the capture or maceration of a specific prey type.
Comments. Stenamma callipygium and S. atribellum are sister species and make up the atribellum species group. The diagnostic character state of this group is the elongate gastral constriction. Stenamma callipygium is easy to distinguish from S. atribellum by its median clypeal tooth and carinulate sculpture.
Material examined. GUATEMALA: Baja Verapaz: Biotopo Quetzal, 15.21329°N, 90.21516°W, 1715m, 8 May 2009; Biotopo Quetzal, 15.21227°N, 90.21430°W, 1750m, 7 May 2009; Ranchito El      Worker diagnosis. Integument mostly dark red-brown to orange-brown; smallsized species (see HL, ML, PrW below); anterior clypeal margin viewed from anterodorsal angle undulating (straight in full-face view), appearing as 2-4 blunt teeth; basal margin of mandible sinuous, with a shallow, but distinct basal depression; head and mesosoma densely sculptured, mostly rugoreticulae; gastral pilosity short, relatively dense, and usually appearing uniformly suberect to subdecumbent, but sometimes more clearly bilayered; petiole somewhat long and gracile, with node relatively small; petiolar and postpetiolar nodes smooth only on anterior faces; eye relatively small (EL 0.08-0.09, , subcircular to oval-shaped, with 4-5 ommatidia in greatest diameter; frontal lobes moderately expanded , mostly to completely covering torular lobes in full-face view; propodeal spines short to medium length (PSL 0.11-0.18, PSI 1.6-2.1). Similar species: Stenamma crypticum, S. cusuco, S. hojarasca. Geographic range. Guatemala to Honduras. Small species; general body color dark red-brown to orange-brown, with patches of dark brown to brown on gaster; appendages lighter, brown to yellow-brown; setae golden brown; mandible with 6 teeth, consisting of 3 distinct apical teeth, a basal tooth, and 2 middle teeth, which are often worn and indistinct; basal margin of mandible sinuous, with a shallow, but distinct basal depression, accompanied by attenuation of cuticle where mandible fits underneath clypeus; mandible mostly smooth and shining, with scattered piligerous punctae and basal striae; anterior clypeal margin viewed at anterodorsal angle undulating (straight in full-face view), appearing as 2-4 blunt teeth; median lobe of clypeus somewhat flattened, longitudinal carinulae absent or very faint, apex with a short transverse carinula; remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions narrow (PCW 0.01-0.03), sides diverging posteriad; frontal lobes moderately expanded , with lateral apices shifted slightly posteriad of torular lobes, which are mostly to completely covered in fullface view; head subrectangular to oval-shaped (CI 82-88), posterior margin slightly depressed medially; eye relatively small (EL 0.08-0.09, REL 14-16), subcircular to oval-shaped, with 4-5 ommatidia in greatest diameter; head mostly rugoreticulate, with a few longitudinal rugae along midline, interstices faintly punctate; scape relatively long (SI 94-104), but variable, either reaching or not quite reaching posterior margin when laid back; scape surface shiny, but somewhat rough, with punctae and faint striae; flagellum with distinct 4-segmented antennal club; mesosoma densely sculptured, except for propodeal declivity, which only has a few faint transverse carinulae; promesonotal dorsum rugose to rugoreticulae, interstices faintly punctate; mesosomal side mostly punctate, with a few rugulae; propodeal dorsum with a few transverse carinae; promesonotum in profile, low-domed, roughly symmetrical; metantoal groove distinct, but somewhat shallow; anterodorsal margin of propodeum in profile with a small welt; propodeal spines present, short to medium length  (PSL 0.11-0.18, PSI 1.6-2.1); petiole somewhat long and gracile (PL/HW 0.53-0.59); petiolar node in profile relatively small (PH/PL 0.49-0.59), asymmetrical, with anterior face long and sloping and posterior face short and nearly vertical, dorsum of node rounded, apex pointing posteriad; postpetiole relatively small (PPH/ PH 0.85-0.91), somewhat dorsoventrally compressed; anterior faces of petiolar and postpetiolar nodes smooth and shiny, remainder of waist mostly punctate, with a few small rugulae around postpetiolar node; gaster mostly smooth and shiny, with scattered piligerous punctae; most of body dorsum with short to moderately long standing pilosity; scape with suberect to decumbent setae; gastral pilosity variable, usually short, relatively dense, and uniformly suberect to subdecumbent, but sometimes clearly bilayered, with a longer suberect layer, and a shorter decumbent layer; setae on legs mostly decumbent to appressed, with some suberect setae on coxae and venter of profemur. Same as worker except for standard queen modifications and as follows: mesoscutum mostly longitudinally rugose, but with a central longitudinal carina that is thick at anterior margin; most of katepisternum and part of anepisternum smooth and shiny; gastral pilosity denser, and more distinctly bilayered.
Male. Unknown. Biology. Stenamma catracho is known only from sifted leaf litter collected from the forest floor. It occurs from approximately 1100-1900 m elevation in montane wet forest habitats.
Comments. Stenamma catracho is most likely to be confused with S. cusuco or S. hojarasca, both of which have expanded frontal lobes and somewhat elongate petioles. Stenamma cusuco can be distinguished easily by its distinctive tridentate clypeal margin, and S. hojarasca can be separated by its longer petiole and completely shiny petiolar and postpetiolar nodes.
There are some morphological differences unique to the Meambar population ( Figure 62) of S. catracho. Meambar specimens have most pilosity longer, with the gastral pilosity clearly bilayered; they have lighter integument color; and they have narrower frontal lobes. The other populations have the pilosity shorter overall and the gastral pilosity denser and not as clearly bilayered. I treat these differences as intraspecific variation until more material is collected.
Molecular phylogenetic data show that S. catracho most likely belongs to a clade that includes S. crypticum, S. monstrosum, and S. saenzae, with S. monstrosum being its sister species (Branstetter unpublished data).   Worker diagnosis. Integument mostly dark brown to brown, rarely black; small-sized species (see HL, ML, PrW below); basal margin of mandible sinuous, with a distinct basal depression; anterior clypeal margin undulating, forming 2-4 blunt teeth; face completely sculptured, mostly rugoreticulate; mesosoma mostly sculptured, except for pronotum, which is usually lightly carinulate-punctate, with a small smooth patch on dorsum and side, but sometimes pronotum completely punctate or mostly smooth; remainder of mesosoma usually strongly punctate; propodeal declivity in profile usually with distinctive outline, in which propodeal lobe is broadly rounded and makes a smooth, sinuous connection with propodeal spine (degree of sinuosity variable); eye of small to moderate size (EL 0.07-0.11, , oval-shaped, with 4-5 ommatidia at greatest diameter; pilosity on gastral dorsum bilayered, with a layer of longer suberect setae, and a denser layer of decumbent setae; propodeal spines tuberculate, or reduced to sharp angles (PSL 0.07-0.09, PSI 1.1-1.4); geography useful in species determination. Small-sized species; general body color usually dark brown to brown, rarely almost black; appendages brown to yellow-brown, becoming lighter toward extremities; in specimens with dark brown to black body color, flagellum sometimes noticeably bright yellow; setae golden brown; mandible with 6 teeth, with basal tooth well defined; basal margin of mandible sinuous, with a distinct basal depression; mandible surface mostly smooth and shiny, with scattered piligerous punctae, and some striations on base and lateral surface; anterior clypeal margin undulating, forming 2-4 blunt teeth, inner teeth often projecting beyond lateral teeth (type population); median lobe of clypeus with a pair of longitudinal carinulae that diverge anteriorly, apex of lobe with a moderately long transverse carinula, area in between median lobe and anterior margin forming a distinct cavity where mandibles insert, remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions of moderate to somewhat narrow width (PCW 0.02-0.04), with sides subparallel to slightly hour-glass shaped; frontal lobes of moderate width , not greatly obscuring torular lobes in full-face view; head roughly oval-shaped (CI 84-92), posterior margin with a slight to distinct median depression; eye of small to moderate size (EL 0.07-0.11, , oval-shaped, with 4-5 ommatidia at greatest diameter; face completely sculptured, mostly rugoreticulate, with some longitudinal carinulae extending back from frontal lobes, interstitial areas with light piligerous punctae; one high-elevation population with facial sculpture more polished, becoming smooth toward posterior margin; scape somewhat short (SI 85-99), not reaching posterior margin when laid back; scape surface mostly smooth, with scattered piligerous punctae; flagellum with a distinct 4-segmented antennal club; mesosoma mostly sculptured, except for pronotum, which ranges from completely punctate to almost completely smooth (both extremes rare); pronotum most often lightly punctate on side, and lightly carinulate-punctate on dorsum, with a small smooth patch in middle (type population); remainder of mesosoma mostly punctate, with some longitudinal carinulae, becoming rugoreticulae on mesonotum; propodeal dorsum and declivity sometimes with transverse carinulae; one high-elevation population with mesopleuron rugulose-punctate, and side of propodeum longitudinally carinulate; promesonotum in profile low-domed and roughly symmetrical; metanotal groove well demarcated, of moderate width and depth; propodeum in profile usually with a distinct profile, in which propodeal lobe has a broadly rounded margin that connects smoothly with propodeal spine; connection usually sinuous, but degree of sinuosity variable; propodeal spines usually tuberculate (type population), but sometimes reduced to sharp angles (PSL 0.07-0.09, PSI 1.1-1.4); petiole in profile of moderate length to slightly elongate (PL/HW 0.49-0.55); petiolar node in profile appearing small (PH/PL 0.52-0.64), and asymmetrical, with anterior face longer and more sloping than posterior face, node dorsum broadly rounded (type population) to more angulate, with apex pointing distinctly posteriad; postpetiole in profile subspherical, usually about same size as petiolar node, but sometimes slighly bulging (PPH/ PH 0.79-1.01); petiole and postpetiole usually mostly punctate, with only anterior faces smooth and shiny, but sometimes nodes almost completely smooth; most of body dorsum with short standing pilosity; setae on face very short, mostly subdecumbent; pilosity on gastral dorsum bilayered, with a sparse layer of longer suberect setae, and a denser layer of decumbent setae, sometimes lower layer very similar in density to upper layer; setae on scape subdecumbent to appressed; setae on legs mostly decumbent to appressed, with some suberect setae on femoral venters and coxae.
Queen description. Same as worker except for standard queen modifications and as follows (comparsion of type population only): pronotum with transverse carinulae/rugulae; mesoscutum mostly smooth, with piligerous punctae, and some longidutinal carinulae along lateral margin; scutellum smooth in middle, rugulose-punctate on lateral margins; mesopleuron mostly smooth; propodeum carinulate-punctate; lower layer of setae on gastral dorsum very dense, almost pubescent; dorsum of mesosoma and anterior faces of petiolar and postpetiolar nodes with a dense layer of short, decumbent setae; propodeal declivity in profile less sinuous, with propodeal lobe smaller and less evenly rounded; wing venation as in Figure 66D.
Male. See Figure 66E-G. Biology. Stenamma connectum is found in montane wet forest habitats from 600-2160 m elevation, and is known almost exclusively from Winkler or Berlese samples of sifted leaf litter. Only once has a nest been found: a single dealate queen with brood underneath a moss mat.
Comments. Distinguishing S. connectum from S. crypticum and S. huachucanum can be difficult. This is because each species is composed of multiple allopatric populations with no clear evidence of sympatry among divergent forms. Using morphology alone, the best solution would probably be to delimit a single widespread species. However, molecular phylogenetic data strongly suggest the existence of multiple biological species (Branstetter unpublished data). As a result, I have decided to delimit several species guided by the combination of morphological and molecular data. Some phenotypically divergent populations which have not been included in the phylogeny may prove challenging to identify.
As currently defined, geography is very useful in separating S. connectum from similar species. Stenamma connectum occurs in the Mexican states of Veracruz and Oaxaca only. Within Oaxaca, it is found along the Caribbean slope in wet forest habitats. Stenamma huachucanum is distributed from the southwestern U.S.A to Oaxaca. Within Oaxaca, it occurs only in the drier habitats in the central and western parts of the state. I consider specimens from Hidalgo and San Luis Potosí states to be S. huachucanum, but some of these specimens are hard to place. Stenamma crypticum occurs mainly from Chiapas, Mexico to Nicaragua; however, a couple of specimens known from one sample collected in Veracruz at 1600 m (11km N San Andrés Tuxtla) appear most like S. crypticum. These specimens lack the broadly rounded propodeal lobes (in profile) and have the promesonotum mostly smooth. Until more material is collected, I treat these as S. crypticum, but I find it possible that they are actually abberant specimens of S. connectum. One specimen that clearly has the characteristics of S. connectum was collected at nearly the same locality, only slightly lower at 1400 m elevation.
Many populations of S. connectum, including the type population, share a set of distinctive morphological character states that distinguish S. connectum from similar species. Key worker characters for the type population are as follows: body color mostly brown; side of pronotum lightly punctate; dorsum of pronotum carinulatepunctate with a small patch of smooth cuticle in middle; mesopleuron and side of propodeum strongly punctate; propodeal declivity in profile forming a sinuous outline, in which the propodeal lobe is broadly rounded and makes a smooth connection with the propodeal spine; propodeal spines tuberculate. The sinuous outline of the propodeal declivity is the most distinctive feature of this species. It is variable among populations, with specimens from lower elevations having the sinuosity more pronounced. Higher elevation populations begin to lose the character state, making these populations more difficult to separate from similar species. Several variants are described below.
Variant 1 ( Figure 65A-C) is known only from the locality Pueblo Nuevo in Veracruz. These specimens differ as follows: smaller overall size; mesosoma completely punctate, with only a few scattered rugulae/carinulae; sinuosity in outline of propodeal declivity pronounced; petiolar node in profile reaching a more angular apex.
Variant 2 ( Figure 65D-F) and variant 3 ( Figure 65G-I) occur along the same elevational transect as the type population, but at mid (~1770 m) and high (> 1900 m) elevations, respectively. Variant 2 differs from the type form in that it has dark brown body color, reduced pronotal sculpture, and a noticeably yellow flagellum. follows: larger size; body color almost black; pronotum almost completely smooth and shiny; mesopleuron rugulose-punctate; side of propodeum carinulate; outline of propodeal declivity not strongly sinuous, with the propodeal lobe often more angular and isolated from the propodeal spine; petiolar and postpetiolar nodes mostly smooth; postpetiole bulging.    Worker diagnosis. Integument dark red-brown to brown; small-sized species (see HL, ML, PrW below); basal margin of mandible sinuous, usually with a small basal depression; anterior clypeal margin undulating, with two small blunt teeth bordering midline; eye of moderate size (EL 0.07-0.11, , oval-shaped, with 4-5 ommatidia at greatest diameter; face mostly rugoreticulate; mesosoma often mostly sculptured, but pronotum variable, usually rugose with smooth patches on dorsum and side, but sometimes mostly rugose or mostly smooth; propodeal spines tuberculate to short (PSL 0.07-0.10, PSI 1.2-1.8); gastral pilosity usually short, dense and clearly bilayered, with a layer of suberect setae and a denser underlying layer of subdecumbent setae, but sometimes setae more uniformly subdecumbent, or suberect setae thickened; geography useful in species determination. Similar species: Stenamma connectum, S. huachucanum, S. ignotum, S. picopicucha. Geographic range. Southern Mexico (Chiapas, Veracruz?) to Honduras. Small-sized species; general body color dark brown to brown or orange-brown, with appendages brown or orange-brown to yellow-brown, becoming lighter toward extremities; setae golden brown; mandible with 6 teeth, inner teeth sometimes worn; basal margin of mandible sinuous, usually with a distinct basal depression, but without tooth; mandible mostly smooth and shining, with scattered piligerous punctae and some basal striae; anterior clypeal margin when viewed from anterodorsal angle undulating, usually forming 2 blunt teeth bordering midline; median lobe of clypeus with a pair of faint longitudinal carinulae that diverge anteriorly, apex of lobe with short transverse carinula; area in between median lobe and anterior clypeal margin forming a shallow concavity where mandibles insert; remaining surface of clypeus mostly smooth; posterior extension of clypeus between antennal insertions somewhat narrow (PCW 0.02-0.04), sides subparallel; frontal lobes of moderate width (FLD 0. , not greatly obscuring torular lobes in full-face view; head subrectangular to oval-shaped (CI 84-91), posterior margin slightly depressed medially; eye somewhat small (EL 0.07-0.11, , oval-shaped, with 4-5 ommatidia at greatest diameter; head completely sculptured, mostly rugoreticulate, with a few longitudinal carinulae along midline; scape relatively short (SI 80-89), not reaching posterior margin of head when laid back; scape surface mostly smooth, with scattered piligerous punctae; flagellum with distinct 4-segmented antennal club, last segment noticeably bulging; pronotal sculpture variable, dorsum usually longitudinally rugose, with a small smooth patch mesad (type population), side usually rugose on upper half and smooth on lower half (type population), sometimes pronotum completely smooth, or completely rugose, with only a small smooth patch on side; dorsum of mesonotum rugulose punctate; katepisternum and side of propodeum punctate, sometimes with a few rugulae; propodeal dorsum punctate, with a few transverse carinulae; propodeal declivity mostly smooth, with a few transverse carinulae on upper half; promesonotum in profile low-domed, and roughly symmetrical; propodeal spines tuberculate to short (PSL 0.07-0.10, PSI 1.2-1.8); petiole usually somewhat short and stocky (PL/HW 0.47-0.54); petiolar node somewhat small (PH/PL 0.56-0.57), roughly symmetrical, dorsum reaching a defined apex, which points nearly vertical; postpetiole in profile variable, usually small and similar in size to petiolar node (type population), but sometimes bulging (PPH/PH 0.91-1.07); petiole and postpetiole usually mostly punctate, with anterior faces of nodes smooth, and posterior faces of nodes with a few rugulae; most of body dorsum with short standing pilosity; pilosity on gastral dorsum usually distinctly bilayered, with a layer of suberect setae, and a slightly more dense layer of decumbent setae (type population), but sometimes setae more uniformly suberect to subdecumbent and less clearly bilayered; suberect layer of setae sometimes slightly thickened; setae on scapes decumbent to appressed; setae on legs mostly subdecumbent to appressed, with longer suberect setae on femoral venters and coxae. Same as worker except for standard queen modifications and as follows: pronotum with transverse carinulae on humeri, becoming smooth mesad; mesoscutum mostly with longitudinal rugulae and foveolae, midline and mesolateral margin smooth; scutellum smooth along midline, and longitudinally carinulate laterad; propodeum with transverse carinulae/rugulae that wrap around surface; mesopleuron mostly smooth; lower layer of setae on gastral dorsum very dense, almost pubescent; wing venation as in Figure 70D.
Male. Unknown. Biology. Stenamma crypticum is a rather common component of the leaf litter in mid-to high-elevation mesic forest habitats in Central America. It has been collected from 900-2800 m, but is most common from 1500-2500 m. Habitat types include cloud forest, mesophyll forest, oak forest, and mixed hardwood forest. Most collections come from samples of sifted leaf litter collected from the forest floor, but some specimens are also known from cookie baits. Nests have never been found, but dealate queens, as well as workers, are common in the leaf litter, suggesting that nests might be in this stratum.
Comments. Stenamma crypticum should be distinguished easily from S. ignotum and S. picopicucha using the diagnostic characters given above. As noted under S. connectum above, separating S. crypticum from S. connectum and S. huachucanum is more challenging. This is because each species comprises a complex of multiple divergent populations, with no clear evidence of sympatry among distinct forms. Using morphology alone, it might be best to name a single species; however, molecular phylogenetic data strongly suggest the existence of at least three species (Branstetter unpublished data). Even though some populations/specimens may prove difficult to identify, I have chosen to delimit these species as best as possible. There are a few key morphological characters that separate the type populations of each species from one another, but when considering all populations, geography is useful.
Stenamma crypticum occurs mainly in Nuclear Central America from Chiapas, Mexico to Honduras, whereas S. connectum is found north of S. crypticum in Veracruz, Mexico and on the wet, Caribbean slope of Oaxaca. Complicating this picture, however, are a few specimens collected from Veracruz at 1600 m (11km N San Andrés Tuxtla). These specimens lack the broadly rounded propodeal lobes characteristic of S. connectum and have a mostly smooth promesonotum. I tentatively identify these specimens as S. crypticum, but I find it possible that they could actually be abberant members of S. connectum, which has been collected close by at a slightly lower elevation (1400 m). The phylogenetic position of the putative S. crypticum specimens has not been assessed. Stenamma huachucanum is distributed from the southwestern U.S.A. to Oaxaca, where it occurs only on the drier western side of the state. A wet forest version of S. huachucanum occurs in eastern Mexico from Tamaulipas to Puebla.
Stenamma picopichuca can be separated from S. crypticum using the diagnostic characters listed above, but I am somewhat uncertain about the phylogenetic placement and status of this species. Stenamma picopichucha has the basal margin of the mandible like S. ignotum and the anterior clypeal margin like S. crypticum. Because of several other similarities, I was originally going to include S. picopicucha in S. crypticum, but I later discovered that the two species occur in sympatry at Cusuco in Honduras. At this site, specimens of S. crypticum clearly have a sinuous basal margin of the mandible and specimens of S. picopicucha have a straight margin. The phylogenetic picopicucha is yet to be tested, and it will be interesting to see if the two species are closely related.
Within the range of S. crypticum there is considerable variation in size, sculpture and gastral pilosity, with some of this variation observable at single sites. At the type locality, for example, I have sampled S. crypticum from 1500 m to about 2200 m elevation. Along this gradient specimens from higher elevation are larger. There is also significant variation in pronotal sculpture within the site, with some specimens having the pronotal dorsum mostly smooth ( Figure 69A-C), and others mostly rugose . At first I tried separating these into distinct forms, but I abandoned this scheme after finding specimens with intermediate phenotypes.
In addition to within site variation, there is considerable among population variation, with almost every population displaying some unique feature. Out of this diversity I describe a couple of variants. Variant 1 ( Figure 69G-I) occurs at several sites in Guatemala (e.g. Biotopo Quetzal, Purulhá). It is similar to the type form, but has a bulging postpetiole and longer gastral pilosity. Variant 2 ( Figure 69J-L) occurs at La Union in Guatemala, with similar-looking specimens at sites in Honduras. Compared to the type form it is smaller and has the suberect layer of gastral pilosity noticeably thickened. Until there is evidence of sympatry, I treat all of this variation as intraspecific.
Material  14.55828°N, 91.19133°W, 2000m, 10 Sep 2008; 4km S Vol. Atitlán, 14.54830°N, 91.19115°W, 1625m, 15 Jun 2009; 4km S Vol. Atitlán, 14.55112°N, 91.19848°W, 1750m, 15 Jun 2009    Worker diagnosis. Integument mostly red-black; small-to medium-sized species (see HL, ML, and PrW below); anterior clypeal margin in full-face view, with three projecting teeth, two well-defined sharp outer teeth, and a blunt central tooth, formed by a projecting median clypeal lobe; anterior clypeal margin underneath median clypeal lobe with two blunt teeth; basal margin of mandible sinuous, with a distinct basal depression, but no basal tooth; frontal lobes markedly expanded , completely obscuring the torular lobes in full-face view; eye of moderate size (EL 0.09-0.11, , with 5-6 ommatidia at greatest diameter; propodeal spines present and of moderate length (PSL 0.16-0.19, PSI 1.8-2.2); gastral setae short, and clearly bilayered, with a layer of suberect setae, and a layer of slightly shorter but denser subdecumbent setae;. Small-to medium-sized species; general body color red black, with patches of brown on gaster; mandibles and appendages lighter, mostly brown to orange-brown; setae pale golden brown; mandible usually with 6 teeth, sometimes with 1-2 small denticles, basal tooth well-defined; basal margin of mandible sinuous, with a distinct basal depression, but no basal tooth; mandible mostly smooth and shiny, with scattered piligerous punctae and basal striae; anterior clypeal margin in full-face view, with three projecting teeth, two well-defined outer teeth, and a more blunt central tooth, formed from a projecting median clypeal lobe; anterior clypeal margin underneath median clypeal lobe with two blunt teeth (only visible with mandibles open and from an anterodorsal view); median clypeal lobe surface usually with a single median longitudinal carinula and a variable number of irregular foveolae, remainder of clypeus smooth and shiny; posterior extension of clypeus between antennal insertions hour- glass-shaped, with middle of hourglass narrow (PCW 0.02-0.03); frontal lobes noticeably expanded , completely obscuring the torular lobes in full-face view; head roughly oval-shaped (CI 83-87), posterior margin with a slight median depression; eye of moderate size (EL 0.09-0.11, , oval-shaped, with 5-6 ommatidia at greatest diameter; head strongly rugoreticulate (not quite foveate), with a few short costae extending back from the frontal lobes and posterior clypeal extension; scape somewhat short (SI 84-89), not reaching posterior margin of head when laid back; scape surface shiny, but somewhat rough, with scattered piligerous punctae, punctulae, and fine striae; flagellum with a somewhat distinct 4-segmented antennal club; mesosoma mostly strongly rugose to rugoreticulate, with finer reticulae, becoming punctae, on pronotal side and anepisternum, rugae near anterior margin of pronotal dorsum usually with a transverse orientation; propodeal dorsum and declivity with transverse carinulae; promesonotum in profile low-domed and roughly symmetrical, but anterior declivity somewhat shorter and steeper; metantoal grove welldemarcated, of moderate width and depth; anterodorsal margin of propodeum with a small welt; propodeal spines present and of moderate length (PSL 0.16-0.19, PSI 1.8-2.2); petiole appearing of moderate length (PL/HW 0.52-0.55); petiolar node relatively small (PH/PL 0.53-0.56), domed, but slightly asymmetrical in profile, with the anterior face longer and more sloping than posterior face; postpetiole subspherical, without a prominent dorsal node; anterior faces of petiolar and postpetiolar nodes smooth and shiny, anterior and lateral sides with a variable number of rugulae and faint punctae; ventral surfaces of waist segments punctate; most of body dorsum with short standing pilosity; setae on scape mostly subdecumbent; gastral setae short, and clearly bilayered, with a layer of suberect setae, and a layer of slightly shorter but denser subdecumbent setae; setae on legs mostly appressed with some suberect setae on coxae and femoral venters.
Queen Same as worker except for standard queen modifications and as follows: pronotum with transverse rugae/rugoreticulae; mesoscutum more rugose than rugoreticulate, with rugae longitudinal in orientation; scutellum with a central patch of smooth cuticle surrounded by longitudinal rugae; mesopleuron partly smooth and shiny.
Male. Unknown. Biology. This species has been collected from only a few samples of sifted leaf litter from the forest floor. It inhabits montane wet forest from approximately 1200-1400 m elevation. The shape of the anterior margin of the clypeus is unique among Stenamma species. Most peculiar is the strongly projecting median lobe, which forms a toothlike protuberance. This trait probably correlates with diet specialization, but nothing is known yet about prey choice in this species.
Comments. The structure of the clypeus is unique among known Stenamma species. Thus, S. cusuco should not be confused with any other species. Although support values are low, molecular phylogenetic results indicate that S. cusuco belongs to a clade that includes S. hojarasca and S. ochrocnemis (Branstetter unpublished data).
Material examined. See type material.   Worker diagnosis. Integument mostly black and shining; medium-sized species (see HL, ML, PrW below); head mostly smooth and shiny; mesosoma reticulately costate to coarsely rugoreticulate; propodeal spines long and robust (PSL 0.28-0.34, PSI 3.0-3.7); frontal lobes dorsolaterally expanded, obscuring the torular lobes in full-face view (FLD 0.25-0.29, FLI 35-38); eye of moderate to large size , oval-shaped, with 7-9 ommatidia at greatest diameter; anterior margin of clypeus with shallow median emargination; basal margin of mandible straight, without a notch or substantial depression; pilosity on gastral dorsum long, flexuous, and relatively sparse. Medium-sized species; general body color black, with mandibles, clypeus and appendages dark brown to yellow-brown; setae golden; mandible with 6 teeth, consisting of 3 distinct apical teeth, a basal tooth, and 2-3 inner teeth, which are often worn and indistinct; basal margin of mandible straight, without a distinct notch or depression; dorsal surface of mandible mostly smooth and shining, with scattered piligerous punctae, and several weak striae extending from base; anterior clypeal margin with shallow median emargination; median lobe of clypeus with a pair of faint carinulae that diverge toward anterior margin, apex of lobe with a faint transverse carinula, remainder of clypeus mostly smooth and shining; posterior extension of clypeus between frontal lobes broad, with subparallel sides (PCW 0.06-0.09); frontal lobes expanded dorsolaterally (FLD 0.25-0.29, FLI 35-38), with torular lobes obscured in full-face view; head roughly oval-shaped, slightly longer than broad (CI 93-97), with posterior margin flat or gently curving, never depressed medially; eyes of moderate size , oval-shaped, with 7-9 ommatidia at greatest diameter; face largely smooth and shining, with faint carinulae and punctae on gena, scattered piligerous punctae elsewhere; scape short, not surpassing posterior margin of head when laid back (SI 84-88); dorsal surface of scape striate; funiculus with distinct 4-segmented antennal club; mesosoma compact, shiny, and almost entirely reticulately costate (specimens vary considerably in sharpness, coarseness, and orientation of costae); propodeal declivity smooth; promesonotum in profile dome-shaped, roughly symmetrical; propodeal spines long and robust (PSL 0.28-0.34, PSI 3.0-3.7), usually projecting dorsoposte- riorly; petiole relatively long and wedge-shaped (PL/HW 0.60-0.65), node variable, appearing rather robust to slightly more gracile, always angled so that the apex points posteriad; anterior slope of petiole usually long and rising gradually from peduncle, but sometimes shorter and rising more abruptly; posterior slope of petiole short and nearly vertical; dorsum of petiolar node viewed from posterior side flat, to depressed medially, to slightly convex; dorsal portion of petiolar node distinctly wider than ventral portion; postpetiolar node in profile smaller than petiolar node (PPH/PH 0.85-0.94), dome-shaped, slightly asymmetrical, with anterior slope longer and more sloping than posterior slope; petiole and postpetiole generally smooth and shiny, nodes with several deep furrows, ventral surfaces faintly punctate; gaster mostly smooth and shiny, with scattered piligerous punctae, and furrows on anterior constriction where gaster inserts into postpetiole; most of body with a relatively sparse layer of long, flexuous setae; setae on scapes and legs varying from mostly suberect to mostly decumbent; setae on femoral venters and coxae always longer and suberect to subdecumbent. Same as worker except for standard queen modifications and the following: costae on mesoscutum with a decidedly longitudinal orientation, but often wavy, and usually with some reticulation anteriorly; costae on side of propodeum longitudinal in orientation; mesopleuron mostly smooth and shiny; wing venation as in Figure 75D.

Stenamma diversum
Male. See Figure 75E-G. Biology. Stenamma diversum occurs in relatively pristine wet forest habitats from sea level to about 1,100 m elevation. It is a particularly interesting species because it has convergently evolved many of the same nesting behaviors as S. alas and S. expolitum, even though it is not closely related (Branstetter 2012, unpublished data). Like these species, S. diversum is a specialist inhabitant of areas dominated by red clay substrate (Branstetter pers. obs.). Nests are commonly found in banks bordering streams or trails, in steep slopes, and sometimes in small patches of vertical clay that form under roots at tree bases. The architecture of a nest of S. diversum is very similar to that of S. alas. The external portion of the nest consists of a small, ear-like turret that is usually sunk into a shallow alcove. At the center of the ear is the nest entrance, which leads to a single, small chamber. Unlike S. alas or S. expolitum, there is only a single nest per colony and colonies are quite small, with a single queen and maybe a dozen workers. Also, S. diversum does not have a "door pebble" to be used to block the nest entrance from predators, as reported by Longino (2005) for S. alas and S. expolitum. Workers of S. diversum are slow moving and appear to be most active during the day. The convergent nature of S. alas and S. diversum nests is striking and begs further investigation into the adaptive significance of these structures. It is possible that the structure is an adaptation to living in very wet, exposed environments. Inside mature S. diversum nests I have often noticed a dark material covering the nest walls. What this material is and what function it serves also needs investigation. Given their nesting habits, it is somewhat odd that the collection of the type series was made "beneath a stone." Perhaps this was on clay bank.
Comments. Stenamma diversum and S. tico are sister species and together form the diversum species group. This group is defined by the following characters: head mostly smooth and shiny; mesosoma mostly reticulately costate; promesonotum in profile lowdomed, roughly symmetrical; postpetiole in profile without a distinct dorsal lobe that projects posteriad over postpetiole (as in S. lobinodus and other lobinodus group species); basal margin of mandible straight; anterior clypeal margin with a median emargination. Based on DNA sequence data S. vexator is likely sister to the diversum species group, but morphological characters could not be found to diagnose the entire clade.
Stenamma diversum is probably the most distinctive Stenamma species, but it does bear some similarity to its sister taxon S. tico and the more distantly related S. lobinodus, both of which share roughly the same color and sculpture pattern. It is easy to separate S. diversum from these other species by comparing the propodeal spines and the frontal lobes. In S. tico, the spines are absent or at most form small dorsally projecting tubercles (PSL 0.14-0.18, PSI 1.4-1.9). In S. lobinodus, the propodeal spines are usually well developed, but they are shorter than those of S. diversum (PSL < 0.23 vs. > 0.27, PSI < 2.6 vs. > 3.0). Stenamma diversum is the only species among these three to have greatly expanded frontal lobes, causing the underlying torular lobes to be covered in full-face view. In the other species, the torular lobes are always visible. The frontal lobes of S. lobinodus are especially reduced. Geography also can help separate these species. Stenamma diversum occurs in sympatry with S. lobinodus only in Oaxaca, Mexico (although never collected together at the same site) and with S. tico only in northern Nicaragua (found in sympatry at Cerro Saslaya and Cerro Musún    Worker diagnosis. Integument mostly orange-brown to brown; small-sized species (see HL, ML, PrW below); anterior clypeal margin often with a deep median excision, but sometimes reduced to a shallow median emargination; basal margin of mandible straight; face densely sculptured and mostly rugoreticulate; mesosoma densely sculptured with punctae, rugae, and/or rugoreticulae; eye small (EL 0.04-0.10, , subcircular, with 2-4 ommatidia at greatest diameter; median portion of clypeus angled dorsoventrally, causing it to be mostly hidden in full-face view; posterior extension of clypeus between antennal insertions very narrow (PCW 0.01-0.03), with border of antennal insertions sometimes touching anteriorly; propodeal spines present, short to long (PSL 0.09-0.20, PSI 1. 8-5.4); pilosity on gastral tergites distinctly bilayered, with a layer of sparse suberect setae (varying in thickness and length), and a layer of decumbent to appressed setae. Similar species: Stenamma saenzae. Small-sized species; general body color mostly orange-brown to brown, with appendages orange-brown to yellow-brown, becoming lighter toward extremities; setae golden; mandible with 5-7 teeth, consisting of 3 distinct apical teeth, a basal tooth, and 1-3 smaller inner teeth/denticles, which are often worn and indistinct; basal margin of mandible straight, without a basal notch or depression; mandible mostly smooth and shiny, with scattered piligerous punctae and some basal striae; anterior clypeal margin often with a deep median excision (type population), but sometimes excision reduced to a shallow emargination; median lobe of clypeus flattened, and angled dorsoventrally, causing it to be mostly invisible in full-face view; surface of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions very narrow (PCW 0.01-0.03), sides subparallel, with border of antennal insertions sometimes touching anteriorly; frontal lobes of moderate width (FLD 0.09-0.14, FLI 19-24), not greatly obscuring torular lobes in full-face view; head appearing subrectangular to oval-shaped (CI [86][87][88][89][90][91][92][93][94], posterior margin flat to slightly depressed medially; eye small (EL 0.04-0.10, , subcircular, with 2-4 ommatidia at greatest diameter; face densely sculptured, usually mostly rugoreticulate and punctate, with some longitudinal rugae along midline (type population), but sometimes mostly rugose; scape of short to moderate length (SI 79-97), usually not reaching posterior margin of head; scape surface mostly smooth, with scattered piligerous punctae; flagellum with a distinct to very distinct 4-segmented antennal club; mesosoma densely sculptured, dorsum of promesonotum ranging from rugoreticulate (type population), to rugose-punctate, to rugose, to mostly punctate, with rugae longitudinal in orientation; side of pronotum usually punctate, with a few rugulae or rugoreticulae (type population), but sometimes mostly rugose, and with a small patch of smooth cuticle; mesopleuron and side of propodeum mostly punctate, with a variable number of rugulae; dorsum and declivity of propodeum with a few transverse carinulae; promesonotum in profile low-domed and roughly symmetrical; metanotal groove usually well-demarcated and somewhat deep; anterodorsal margin of propodeum often raised into a small to large welt, but sometimes average; propodeal spines present, short to long (PSL 0.09-0.20, PSI 1. 8-5.4); petiole appearing moderate to slightly elongate (PL/HW 0.45-0.56), usually with a distinct node, but sometimes node less distinct, making petiole look more wedge-shaped; when distinct, petiolar node in profile, average to slightly enlarged (PH/PL 0.48-0.64), and roughly symmetrical, dorsum of node usually gently rounded and pointing vertically (type population), but sometimes broadly rounded, or nearly angulate and pointing slightly posteriad; postpetiole in profile usually subspherical and appearing similar in size to petiolar node (PPH/PH 0.79-0.96), postpetiole in dorsal view often distinctly wider than petiole, sometimes much wider (PPW/PW 0.55-0.83); petiole and postpetiole usually mostly punctate, with only the anterior faces of nodes smooth, but sometimes nodes completely smooth, or completely punctate; gaster mostly smooth and shiny, with scattered piligerous punctae; most of body dorsum with standing pilosity; pilosity on gastral tergites distinctly bilayered, with a layer of sparse suberect setae (varying in thickness and length), and a layer of decumbent to appressed setae; setae on scapes and legs mostly decumbent to appressed, with some longer suberect setae on femoral venters and coxae. Same as worker except for standard queen modifications and as follows (comparison with worker and queen from type population only): pronotum rugoreticulate laterad, and punctate mesad; mesoscutum and scutellum rugoreticulate to foveate; propodeum with transverse carinulae that wrap around surface; katepisternum mostly smooth; petiole more elongate.

Biology.
A rather uncommon species known almost exclusively from Winkler and Berlese samples of sifted leaf litter, except for one collection from under a stone. Stenamma excisum has been collected from 60-2280 m elevation and occurs in a variety of wet forest environments (e.g. tropical rainforest, cloud forest, disturbed mesophyll forest, pine-oak forest, riparian wet forest). The excision in the anterior clypeal margin of most specimens is unique and suggests some sort of diet specialization different from other Stenamma species.
Comments. Although quite variable across its range (see below), S. excisum is separable from similar species using the characters in the key and diagnosis. Several species are superficially similar to S. excisum, but no other species has the same unique clypeal structure. Phylogenetic results indicate that S. excisum is sister to S. lagunum and that this clade is sister to the remainder of MAC Stenamma species (Branstetter 2012, unpublished data).
Stenamma excisum forms a difficult species complex composed of several allopatric variants, which probably constitute distinct species. The type form is known only from two sites in Honduras, where it is unusually abundant in leaf litter samples. The most important features of this form are the rugoreticulate sculpture on the pronotal dorsum and the nearly triangular excision in the anterior clypeal margin. Other characteristics specific to this form are indicated in the species description above (see parenthetical comments). Specimens from the populations in Honduras and the next closest population are quite divergent from one another. Furthermore, the type form seems to be confined to lower elevations, whereas the other variants usually occur at mid elevations. For these reasons, I highly suspect that there are multiple species within S. excisum as it is described here. However, too few collections have been made in intervening areas to adequately assess variation and species boundaries.
Variant 1 ( Figure 78A-C) is known mainly from mid-elevation sites along the wet eastern slopes of the mountains in Oaxaca, Mexico, but a single specimen is also known from Nahá in Chiapas, Mexico. This variant is very similar to the type population, but differs as follows: smaller overall body size; body color darker, mostly dark orange-brown; sculpture on pronotal dorsum longitudinally rugose, without reticulae.
Variant 2 ( Figure 78D-F) occurs in the same area as variant 1, but the two forms have not been collected together. It is similar to variant 1 except for the following: anterior clypeal margin with a shallow median emargination, lacking a deep excision; propodeal spines in profile longer and somewhat sinuous; anterior margin of propodeal dorsum with a more distinct welt; postpetiole in dorsal view much wider than petiolar node (PW/PPW 0.55-0.61).
Variant 3 ( Figure 78G-I) is known from a single aberrant specimen collected near variant 2, but from a slightly higher elevation. It differs from variant 2 as follows: anterior clypeal margin intermediate between variant 1 and 2, with a shallow excision; propodeal spines short, almost tuberculate; antennal segments 11 and 12 noticeably bulging; postpetiolar node mostly smooth; postpetiole in dorsal view not greatly expanded; upper layer of setae on gastral dorsum shorter, sparser, and subdecumbent.
Variant 4 ( Figure 78J-L) is found mainly in northern Mexico in Tamaulipas (El Cielo) and Nuevo León (Monterrey de Chipinque) states. It is a very small version of S. excisum and is quite divergent from the type population. I originally intended to describe it as a separate species, but later found intermediate-looking specimens from allopatric populations in Querétaro and Veracruz, Mexico. It differs from the type population as follows: overall body size much smaller; sculpture reduced; face with only light rugoreticulae, punctae, and carinulae; dorsum of pronotum with sparse longitudinal carinulae, interstices shiny; propodeal spines short; decumbent layer of pilosity on gastral dorsum sparse, suberect layer slightly thickened.
Variant 5 ( Figure 79A-C) occurs in Veracruz, Mexico. It is intermediate between the type population and variant 4. It differs from variant 4 as follows: head and body densely punctate; dorsum of pronotum with longitudinal rugulae/carinulae, but interstices punctate; petiolar node reaching a sharper apex, which points distinctly posteriad; suberect layer of pilosity on gastral dorsum (and most of body dorsum) longer. Variant 6 ( Figure 79D-F) is known from two localities in Veracruz, Mexico (Paraje Nuevo, Tetzonapa). It is similar to variant 5, but differs as follows: anterior clypeal margin with a median emargination, lacking an excision; body larger and with distinctly elongate appendages; decumbent layer of gastral pilosity very sparse.
Variant 7 ( Figure 79G-I) is known from a single locality in Nuevo León, Mexico (38 km SSW Monterrey). It is very similar to variant 4, but differs as follows: anterior clypeal margin with a median emargination, lacking a deep excision; larger overall size; head larger, more robust, with a distinct median depression in posterior margin; petiolar node in profile broadly domed and more asymmetrical, with a longer more sloping anterior face.   Worker diagnosis. Integument mostly black to dark red-brown; medium-sized species (see HL, ML, PrW below); petiole and postpetiole almost completely smooth and shiny, with only a few faint vestigial punctae sometimes present; postpetiole in profile bulging, globular, appearing more voluminous than petiolar node; face with a fan of carinae/rugae extending from frontal lobes to approximately ¾ distance to posterior margin of head, remainder of head smooth and shiny; dorsum of promesonotum with distinctive transverse furrows that reticulate toward posterior margin; propodeal spines absent to tuberculate (PSL 0.13-0.14, PSI 1.0-1.1), dorsal and declivitous faces of propodeum in profile flat, forming a blunt 90° angle; eye relatively large (EL 0. REL 19), with 8 ommatidia at greatest diameter; anterior clypeal margin with median emargination; basal margin of mandible straight; gastral setae long, sparse, and uniformly suberect. Medium-sized species; general body color black to dark red-brown, with brown patches on gaster; appendages mostly brown, changing to yellow-brown at extremities; setae golden brown; mandible with 5-7 teeth, consisting of 4 distinct apical teeth, a distinct basal tooth, and 1-2 worn denticles in between; basal margin of mandible straight, without a basal notch or depression; mandible surface with scattered piligerous punctae and faint striae; anterior clypeal margin with a median emargination; median lobe of clypeus obliquely flattened, mostly smooth and shiny, with a short transverse carinula near anterior margin, remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions somewhat wide (PCW 0.07-0.08), with sides subparallel; frontal lobes somewhat narrow (FLD 0.0.21-0.24, FLI 29-31), not obscuring torular lobes in full-face view, outer margin of frontal lobes nearly parallel, almost without a discernable lateral apex; head subrectangular to oval-shaped (CI 92-94), with posterior margin flat, not depressed medially; eye relatively large (EL 0. , oval-shaped, with 8 ommatidia at greatest diameter; face with a fan of coarse carinae or costae extending from the frontal lobes to no more than ¾ distance to posterior margin of head; gena with short rugae and rugoreticulae; remainder of head mostly smooth and shiny; scape of moderate length (SI 85-88), not quite reaching posterior margin of head when laid back; scape surface mostly smooth and shiny, with scattered piligerous punctae; flagellum with distinct 4-segmented antennal club; mesosoma densely sculptured, except for a patch of smooth, shiny cuticle on side of pronotum and katepisternum; dorsum of promesonotum with distinctive transverse furrows, which merge together posteriad and appear reticulate; sculpture on propodeum costate to rugose, with orientation transverse on dorsum, and longitudinal on side; mesopleuron rugose; propodeal declivity with faint transverse carinulae; promesonotum in profile low-domed and roughly symmetrical; metanotal grove somewhat indistinct and wide; propodeal spines absent to tuberculate (PSL 0.13-0.14, PSI 1.0-1.1), appearing in profile as a blunt 90° angle that separates dorsal and declivitous faces of propodeum; petiole of moderate length (PL/HW 0.52-0.56); petiolar node in profile robust and somewhat bulging (PH/PL 0.56-0.59), asymmetrical, with a longer more sloping anterior face and a short almost vertical posterior face; node dorsum flat to gently rounded and pointing posteriad; postpetiole in profile large, bulging, appearing slightly more voluminous than petiolar node, outline asymmetrical, with the anterior face longer and more gently sloping, and the posterior face short and vertical, dorsum of node broadly rounded; petiole and postpetiole mostly smooth and shining; gaster mostly smooth and shiny, with scattered piligerous punctae, and very short furrows around anterior constriction; most of body dorsum with long standing pilosity; scape setae suberect to subdecumbent; gastral setae long, somewhat sparse, and uniformly suberect; setae on legs suberect to subdecumbent, with longer suberect setae on coxae and femoral venters.
Queen. Unknown. Male. Unknown. Biology. Stenamma expolitico is known from only four specimens, collected from sifted leaf litter in wet forest between 500-1100 m elevation.
Comments. Stenamma expolitico belongs to the expolitum species group, which also includes S. alas and S. expolitum (a diagnosis for this group is given under S. expolitum below). Stenamma expolitico can be separated from S. alas and S. expolitum by the presence of transverse furrows on the promesonotal dorsum, and by the shape of the propodeum in profile, which in S. expolitico forms a blunt 90° angle where the dorsal and declivitous faces meet.
I am not completely convinced that S. expolitico is a good species because it is known from only a few workers and is somewhat intermediate in morphology between S. expolitum and S. tico. It could be a hybrid form, or a rare variant of S. expolitum or S. alas. I choose to recognize it as separate species here, because, although rare, it does occur at several sites in sympatry with the other expolitum group species, and it is easily identifiable. Furthermore, many nests of S. alas and S. expolitum have been excavated, and workers with S. expolitico-like morphology have never been found. More material of S. expolitico, especially from nest series, is needed to test this hypothesis and confirm its status as a real biological species.

Stenamma expolitum
Medium-sized species; general body color black to dark red-brown, with patches of dark brown on gaster; appendages mostly dark brown with joints and extremities a lighter orange-brown; setae dark golden brown; mandible usually with 6-7 teeth, consisting of 4 distinct apical teeth, a distinct basal tooth, and 1-2 inner teeth/denticles, which are usually worn and indistinct; basal margin of mandible straight, without a basal notch or depression; mandible surface mostly smooth and shiny, with scattered piligerous punctae and a few faint striae; anterior clypeal margin with median emargination; median lobe of clypeus obliquely flattened, mostly smooth and shiny, except for transverse carinula near anterior margin, remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions somewhat wide (PCW 0.05-0.08), with sides subparallel to slightly diverging posteriad; frontal lobes of moderate width , not covering torular lobes in fullface view; head roughly oval-shaped (CI 87-92), with posterior margin flat, not depressed medially; eye relatively large (EL 0. , oval-shaped, with 7-9 ommatidia at greatest diameter; face completely smooth and shiny, except for variable number of very faint carinulae extending from frontal lobes to about midpoint of head, a few carinulae on gena, and scattered piligerous punctae; scape of moderate length (SI 91-96), usually reaching posterior margin of head when laid back; scape surface mostly smooth and shiny, with scattered piligerous punctae; funiculus with distinct 4-segmented antennal club; mesosoma almost completely smooth and shiny, except for transverse carinulae on propodeal dorsum, carinae along metanotal grove, and a few scattered rugulae and piligerous punctae; metanotal grove somewhat shallow and wide; propodeal dorsum in profile flat to distinctly convex; propodeal spines absent, at most forming nearly imperceptible nubs (PSL 0.12-0.14, PSI 0.9); petiole of moderate length (PL/HW 0.53-60); petiolar node in profile robust (PH/PL 0.54-0.60), wedge-shaped, with the anterior face long and sloping and the posterior face shorter and nearly vertical; node dorsum rounded, pointing vertically or slightly posteriad; petiolar node in profile robust, more globular than petiolar node, but similarly asymmetrical with long anterior face and short vertical posterior face; petiole and postpetiole mostly smooth and shining, with a few vestigial punctae; gaster smooth and shiny, with only scattered piligerous punctae; most of body dorsum with long standing pilosity; scape setae suberect to subdecumbent; setae on gastral tergites long, sparse, and uniformly suberect; setae on legs suberect to subdecumbent, with longer suberect setae on coxae and femoral venters.  (60), .
Same as worker except for standard queen modifications and the following: facial sculpture more developed, with distinct carinulae extending from frontal lobes to ocelli, and some carinulae on gena; pronotum with transverse striae near posterior margin; posterior third of mesoscutum with variable amount of striae/costae, orientation variable, most often longitudinal, but sometimes transverse, or obliquely angled mesad toward posterior margin; scutellum with variable number of longitudinal costae; propodeum with more distinct transverse carinae that extend across the dorsum to upper half of side; wing venation as in Figure 84D.
Male. See Figure 84E-G. Biology. Stenamma expolitum is a specialist inhabitant of clay banks. It occurs from 50-1300 m elevation in mature wet forest environments. Nests are generally found in vertical clay banks along streams or cuts along trails. The biology of S. expolitum is reviewed in detail in Longino (2005) and in the overview of natural history section above. Also, see also the biology section for S. alas above. These two species have nearly identical behaviors with subtle modifications, which I describe here. Stenamma expolitum constructs its nests with a vertical turret, rather than a horizontal one. Each nest usually has two chambers instead of one. The main chamber connects to the turret, but there is often a secondary chamber behind the turret. The queen and brood always occur in the main chamber. Colony size is probably similar to S. alas, but so far, censused colonies tend to be smaller, with around 100 individuals. In Costa Rica, I have noticed that S. expolitum can be abundant at very low elevations, whereas S. alas is more common around 300 m and higher. It also seems to be easier to find colonies of S. expolitum away from streams in trail cuts or in steep clay slopes, suggesting that the species may be more tolerant of drier substrates.
Comments. Stenamma expolitum, along with S. alas and S. expolitico, belongs to the expolitum species group. This group is defined by the following: propodeal spines absent; petiole and postpetiole almost completely smooth and shiny, with only faint punctae sometimes present laterally; postpetiole in profile bulging, globular, appearing more voluminous than petiolar node; anterior clypeal margin with a median emargination; basal margin of mandible straight. Molecular phylogenetic data firmly show that S. zelum is sister to the expolitum group (Branstetter 2012), but this species is morphologically divergent and shares none of the expolitum group's diagnostic character states.
Stenamma expolitum can be separated from other expolitum group species by its nearly completely smooth and shiny face. In the field, S. expolitum can be separated from S. alas by its nest structure, described above. Although they do not co-occur, S. expolitum looks superficially like S. atribellum, which is restricted to Cusuco, Honduras. Both species have completely smooth sculpturing, but the latter species has the anterior constriction of the gaster distinctly elongate. Stenamma felixi Mann, 1922: 21, fig. 10  Medium-to large-sized species; general body color mostly black to dark brown, with appendages lighter, brown to orange-brown toward extremities; setae dark goldbrown; mandible with 5-6 teeth, consisting of 4 distinct apical teeth, a basal tooth, and 1 tooth in between, which is smaller and often effaced; basal margin of mandible straight to slightly sinuous, without a basal notch or depression; mandible mostly smooth, except for scattered piligerous punctae, and some lateral striations; anterior clypeal margin with a shallow median emargination; median lobe of clypeus with at least a pair of distinct longitudinal carinulae that diverge toward anterior margin, sometimes with a few additional faint carinulae, apex of lobe smooth, or with some faint transverse carinulae; remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between frontal lobes of moderate width (PCW 0.04-0.09), sides subparallel to slightly hour-glass-shaped; frontal lobes of moderate width , not greatly obscuring torular lobes in full face view; head usually roughly oval-shaped, but some populations with posterior margin distinctly broader than anterior margin, making head appear more triangular (CI 83-90), posterior margin always depressed medially; eye relatively large , oval-shaped, with 8-11 ommatidia at greatest diameter; face densely sculptured, but sculpture type variable, most often with some longitudinal rugae/carinae along midline, transitioning to rugoreticulae toward lateral margins, but sometimes face almost completely rugoreticulate, or completely carinate, depth and sharpness of sculpture variable; scape of moderate length (SI 84-101), just reaching posterior margin of head when laid back; scape surface mostly smooth, but with distinct carinulae, and scattered piligerous punctures; scape sometimes appearing thickened and more robust; flagellum with distinct 4-segmented antennal club; mesosoma mostly densely sculptured, but sculpture type variable; dorsum of pronotum usually rugose (longitudinal orientation) to rugoreticulate, but sometimes carinate, anterior declivity of pronotum with transverse carinulae; dorsum of mesonotum rugoreticulate to transversely carinate, sometimes intermediate; side of pronotum rugulose to carinate; katepisternum mostly smooth, with some rugulae on upper half; dorsum and declivity of propodeum transversely carinate/carinulate; side of propodeum rugose; promesonotum in profile domed (higher than average), symmetrical to slightly asymmetrical, with location of apex variable; metanotal groove distinct, but narrow; dorsum of propodeum in profile distinctly longer than declivity; propodeal spines absent, propodeum forming shallow, blunt angles where dorsum and declivity converge (PSL 0.07-0.11, PSI 0.8-1.1); petiole of moderate length (PL/HW 0.48-0.55); petiolar node of moderate height (PH/PL 0.60-0.64), subconical in shape, usually pointing vertically to only slightly posteriad, dorsum narrowly to somewhat broadly rounded, posterior margin of petiole, where postpetiole inserts, distinctly bent downwards; postpetiole in profile nearly symmetrical, with anterior face slightly longer than posterior face, postpetiole similar in size to petiolar node (PPH/PH 0.78-0.85); petiole and postpetiole usually mostly punctate, with only anterior faces of nodes smooth, but sometimes nodes mostly smooth, with punctae faint; gaster smooth, with scattered piligerous punctae; most of body dorsum with standing pilosity; setae on gastral tergites mostly sparse, long, and suberect, only sometimes with a few short decumbent setae; setae on scapes subdecumbent to appressed; setae on legs decumbent to appressed, with a few suberect setae on femoral venters and coxae. Same as worker except for standard queen modifications and as follows: pronotum transversely carinulate; mesoscutum longitudinally carinulate, or carinate; scutellum rugoreticulate, or longitudinally carinulate to carinate; propodeum with transverse carinulae/carinae that wrap around surface; mesopleuron usually mostly smooth; pilosity on gastral tergites clearly bilayered, with a sparse layer of long, suberect setae, and a dense layer of appressed pubescence; wing venation in Figure 88D.
Male. See Figure 88E-G. Biology. Stenamma felixi is one of the most widespread and common species of MAC Stenamma. It occurs from approximately 50-1600 m, but is most common above 500 m, and is always found in wet forest environments, ranging from lowland rainforest to cloud forest. Workers have been collected by sifting leaf litter, beating and sweeping vegetation, baiting, using pitfall and Malaise traps, and by general searching. Nests are generally quite large and have been found in rotting logs on the ground, in tree stumps, under bark of logs, and rarely in mud banks. A few lone foundresses have been found under rotting epiphyte clumps in old treefalls, and some workers have been collected from orchids at quarantine in the U.S. All colonies collected so far have been monogynous. Workers seem to be epigeic, solitary foragers, but nothing is known about dietary preference. A very common experience is to find lone, stray workers running across medium-to large-sized logs in forest.
Comments. This species is rather distinctive with its large size, lack of propodeal spines, and dense sculpturing. It should not be easily confused with any other MAC species.
Over its range, S. felixi shows considerable variation in the density and orientation of its sculpturing as well as in petiole shape. However, I have only identified one distinct variant (Figure 87) worth describing in more detail. Specimens from Nicaragua and Costa Rica have very deep carinate sculpturing on the face and mesosoma. The facial carinae are usually longitudinal, but occasionally reticulate laterad. The pronotal dorsum has longitudinal carinae, but the side of the pronotum has arcuate carinae that wrap across the dorsum of the metanotum. The head in profile view has a very distinctive shape, in which the posterior margin of the head is very wide compared to the anterior margin, giving the head a somewhat triangular appearance. Lastly, the petiolar and postpetiolar nodes are noticeably smooth. Specimens from Colombia and Ecuador and from north of Nicaragua lose the carinate sculpture. I treat all of the slight      Worker diagnosis. Integument mostly dark red-brown to orange-brown; smallto medium-sized species (see HL, ML, and PrW below); anterior clypeal margin undulating, with 4 blunt teeth; basal margin of mandible straight to slightly sinuous, without a basal notch or deep depression; gastral pilosity clearly bilayered, with a layer of suberect setae, and a layer of decumbent setae; petiole distinctly elongate (PL/HW 0.60-0.68); postpetiolar node dorsoventrally flattened and slightly elongate (PPH/ PH 0.75-0.84); eye relatively small (EL 0.07-0.11, , subcircular, with 4-5 ommatidia at greatest diameter; median clypeal lobe projecting dorsally outward, resulting in rather distinct dorsal and anterior surfaces (visible in profile); dorsal surface of median lobe with a pair of distinct longitudinal carinulae that strongly diverge around median lobe at anterior margin; frontal lobes slightly to very strongly expanded , either completely or mostly covering torular lobes in full-face view; propodeal spines present, short to moderate length (PSL 0.12-0.17, PSI 1.6-1.9). Small-to medium-sized species; general body color dark red-brown to orange-brown, with patches of lighter brown on gaster; appendages orange-brown to yellow-brown; setae pale golden brown; mandible with 5-7 teeth, consisting of 3 distinct apical teeth, a distinct basal tooth, and 1-3 worn or denticulate inner teeth; basal margin of mandible straight to slightly sinuous, without a basal notch or deep depression; mandible mostly smooth and shiny, with scattered piligerous punctae and faint striae; median clypeal lobe projecting dorsally outward, resulting in rather distinct dorsal and anterior surfaces (visible in profile); anterior clypeal margin undulating, with 4 blunt teeth (best viewed at an anterodorsal angle); dorsal surface of median lobe with a pair of distinct longitudinal carinulae that strongly diverge around median lobe at anterior margin; remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions nar-row (PCW 0.03), with sides subparallel to hourglass-shaped; frontal lobes slightly to very strongly expanded , either completely or mostly covering torular lobes in full-face view; frontal carinae weakly developed, not extending beyond frontal lobes; head subrectangular to somewhat oval-shaped (CI 82-88), posterior margin slightly depressed medially; eye appearing small (EL 0.07-0.11, , subcircular, with 4-5 ommatidia at greatest diameter; head strongly rugoreticulate, with a few longitudinal costae along midline, interstices faintly punctate; scape somewhat short (SI 82-89), not reaching posterior margin of head when laid back; scape surface mostly smooth and shiny, with scattered piligerous punctae; flagellum with a somewhat distinct 4-segmented antennal club; mesosoma completely sculptured, except for propodeal declivity, which has faint transverse carinulae; promesonotal dorsum rugose to rugoreticulate and punctate, with rugae transverse near anterior margin, becoming arcuate, and then longitudinal posteriad; mesosomal side mostly punctate, with scattered rugulae; anterodorsal margin of promesonotum with a somewhat distinct straight to lightly curving transverse carina, anterolateral margins of pronotum forming distinct shoulders in dorsal view; anterior declivity of pronotum in profile nearly vertical, and forming a sharp transition with the dorsum; promesonotum in profile low-domed, somewhat asymmetrical; metanotal grove distinct, deeper than average; anterodorsal margin of propodeum with a distinct welt; propodeal spines present, short to moderate length (PSL 0.12-0.17, PSI 1.6-1.9); petiole distinctly elongate and gracile (PL/HW 0.60-0.68); petiolar node relatively small (PH/ PL 0.45-0.49), subconical and roughly symmetrical in profile, with a rounded dorsum; postpetiolar node dorsoventrally flattened and slightly elongate (PPH/PH 0.75-0.84); petiolar and postpetiolar nodes almost completely smooth and shining, remaining surfaces of waist segments mostly punctate, with a few rugulae surrounding postpetiolar node; gaster mostly smooth and shiny, with scattered piligerous punctae; most of body dorsum with short standing pilosity; gastral pilosity clearly bilayered, with a layer of suberect setae, and a layer of decumbent setae; scape setae decumbent to appressed; setae on legs mostly decumbent to appressed, with suberect setae on coxae and femoral venters.
Queen. Unknown. Male. Unknown. Biology. Stenamma hojarasca is a rare species known almost exclusively from sifted leaf litter collected from the forest floor. The only exception is a single specimen from a carrion baited pitfall trap in Belize. This species is found in montane mesophyll and cloud forest habitats and has been collected from 1100-1550 m elevation.
Comments. The form of the waist segments combined with the projecting median clypeal lobe, make S. hojarasca a very distinctive species. It should not be confused easily with any other MAC species.
The most significant form of variation within this species is the extent to which the frontal lobes are expanded. In the Cusuco population, the frontal lobes are greatly expanded laterally and anteroposteriorly, completely covering the torular lobes in full-face view. In the other populations, the frontal lobes are only moderately expanded and they do not completely cover the torular lobes in full-face view, leaving the outer margins somewhat visible. I treat this as intraspecific variation until more material can be gathered.    Worker diagnosis. Note this species is variable and difficult to characterize globally. See comments section below, discussing population variants. Integument mostly dark brown to brown; small-sized species (see HL, ML, PrW below); basal margin of mandible sinuous, with a distinct basal depression, but no tooth; anterior clypeal margin undulating, forming 2-4 blunt teeth; eye of moderate size (EL 0.07-0.12, REL [14][15][16][17][18][19][20][21], oval-shaped, with 4-8 (usually 5-6) ommatidia at greatest diameter; propodeal spines tuberculate to short (PSL 0.06-0.11, PSI 1.0-1.4); face usually completely sculptured, with carinulae, rugoreticulae and punctae, but some populations with posterior ¼ or less of head smooth and shiny; pronotal sculpture variable, often with some carinulae and punctae, but some populations completely smooth; remainder of mesosoma sculptured, with punctae, carinulae and/or rugulae; propodeal lobe in profile usually isolated from propodeal spine and with angulate corners, but some populations with lobe appearing broadly rounded and forming a smooth connection with propodeal spine; geography is useful in species determination. Small-sized species; general body dark brown to brown (type population), with appendages brown or orange-brown to yellow-brown, usually lighter at joints and toward extremities; setae golden brown; mandible with 6-7 teeth, 2-3 teeth near basal tooth sometimes worn and indistinct; basal margin of mandible sinuous, with a distinct basal depression, but no tooth; mandible mostly smooth and shiny, with some scattered piligerous punctae, and some striations near base and on lateral surface; anterior clypeal margin undulating, forming 2-4 sharp to blunt teeth (4 sharp teeth in type population); median lobe of clypeus with a pair of longitudinal carinulae that diverge toward anterior margin, apex with a short transverse carinula, area in between median lobe and anterior clypeal margin forming a shallow concavity; remaining surface of clypeus mostly smooth; posterior extension of clypeus between antennal insertions somewhat narrow to moderate width (PCW 0.03-0.05), with sides subparallel; frontal lobes of moderate width , not greatly obscuring torular lobes in full-face view; head subrectangular to roughly oval-shaped (CI 83-92), posterior margin slightly depressed medially; eye of moderate size (EL 0.07-0.12,  , oval-shaped, with 4-8 (usually 5-6) ommatidia at greatest diameter; face sculpture variable, usually completely sculptured, with light rugoreticulae, longitudinal carinulae, and/or punctae, but sometimes sculpture reduced, with posterior 1/4 or less of head becoming smooth and shiny; scape of short to moderate length (SI 81-94), usually not quite reaching posterior margin of head when laid back; scape surface mostly smooth to somewhat rough (type population), with variable density of piligerous punctae; flagellum with a distinct 4-segmented antennal club; pronotal sculpture highly variable, often with some longitudinal carinulae/rugulae and faint punctae (type population), but some populations completely smooth; remainder of mesosoma completely sculptured with punctae and a variable amount of rugulae/carinulae; promesonotum usually low-domed, and asymmetrical, with the anterior face longer and steeper than posterior face (type population), but some populations with promesonotum distinctly domed, and roughly symmetrical; metantoal groove present and distinct, of average width and depth; propodeal lobe in profile usually isolated from propodeal spine and with angulate corners, but some populations with lobe appearing broadly rounded and forming a smooth connection with propodeal spine; propodeal spines tuberculate to short (PSL 0.06-0.11, PSI 1.0-1.4); petiole length and shape variable, often short and stocky, with a somewhat large node that points vertically, and a sinuous venter (type population), but sometimes more elongate, with node smaller and pointing distinctly posteriad, or sometimes anteroposteriorly compressed, making it very narrow (PL/HW 0.46-0.59); postpetiole usually forming a small node, similar in size or smaller than petiolar node (type population) (PPH/PL 0.79-0.97); petiole and postpetiole usually mostly punctate, with only anterior faces of nodes smooth (type population), but some populations with punctae reduced and nodes mostly smooth; gaster usually completely smooth, but some populations with first sternite and tergite lightly to strongly punctate (variable in type population); most of body dorsum with relatively short standing pilosity; gastral pilosity distinctly to indistinctly bilayered, with a layer of longer suberect to subdecumbent setae, and a layer of decumbent setae, density of setae variable, usually relatively dense (type population); setae on scape decumbent to appressed; setae on legs decumbent to appressed with longer setae on femoral venters and coxae. rugulae; mesoscutum longitudinally carinulate, with a small patch of smooth cuticle anteromesad; scutellum smooth along midline, with longitudinal rugulae mesad; anepisternum partly smooth, remainder carinulate; katepisternum mostly smooth; propodeum with transverse carinulae that wrap around propodeum; propodeal spines longer than worker; gastral pilosity denser; wing venation as in Figure 95D.
Male. Unknown. Biology. Stenamma huachucanum is a cryptic leaf litter ant known mostly from Winkler or Berlese samples of sifted leaf litter. As defined here, the species is widely distributed, occupying both relatively dry, seasonal habitats (e.g. tropical deciduous forest with juniper, oak-pine-juniper woodland, oak woodland, oak-pine-douglas fir forest) and tropical wet forest habitats (e.g. mesophyll forest, cloud forest, oak-pine forest). Collections have been made from 1000-2900 m, but the species is most common between 1600-2500 m. In seasonal habitats, workers have been found underneath rocks, in addition to the leaf litter.

Comments.
Stenamma huachucanum forms a difficult complex composed of many divergent allopatric populations. The complex probably includes several good biological species, but I have chosen to lump most forms into a single entity, because there is no clear evidence of sympatry among forms, and some specimens appear to have intermediate phenotypes that connect distinct forms. The exceptions to this lumping approach are the similar species S. connectum and S. crypticum. These species are morphologically similar to S. huachucanum, but molecular phylogenetic results provide strong evidence that they represent separate lineages (Branstetter unpublished data).
There are some key morphological differences separating populations of S. huachucanum from S. connectum and S. crypticum, but considering all of the variation among populations, the easiest way to identify species is with geography. Stenamma huachucanum occurs from the southwestern U.S.A to Oaxaca, where it is found only in the drier, interior of the state. In eastern Mexico, the species is found from Tamaulipas to Puebla, with no records from Veracruz. Stenamma connectum is found in Veracruz, Mexico and on the wetter, Caribbean slope of Oaxaca. Stenamma crypticum occurs mainly from Chiapas, Mexico to Nicaragua. However, as noted above under both S. crypticum and S. connectum, a few putative S. crypticum specimens are known from one sample taken in Veracruz, nearly in sympatry with S. connectum. If confirmed, this latter case is the only evidence of sympatry among any of these similar-looking species.
Within the S. huachucanum complex there is considerable variation among populations. To help in the identification of S. huachucanum, and to aid future taxonomic efforts, I describe several S. huachucanum variants below. One observation about variation within the complex is that specimens from western and central Mexico, where it is drier, tend to look more like the type population. Specimens from the eastern slope, where it is wetter, become smoother and more aberrant, in general. The most problematic areas are in central Mexico where it transitions from wet to dry. At these localities I find specimens with intermediate features. This is one of the main reasons I have lumped what seem like very different populations together.
The main features of the type form of S. huachucanum are indicated in the species description above (see parenthetical comments). The key characters for the type form are sculpturing and the shape of the petiole. The head is completely sculptured and mostly rugoreticulate-punctate, with some longitudinal carinulae along the midline. The pronotum is lightly carinulate-punctate (longitudinal orientation), with small smooth patches on the dorsum. One characteristic unseen by Smith (1957) or Snelling (1973) is that some specimens of S. huachucanum from the southwestern U.S.A. have the first gastral tergite and sternite punctate. I treat this as intraspecific variation as no other characters within these specimens vary significantly. The petiole of the type form has a distinctive shape, shared by several of the variants. It is rather short in length, but with a tall vertically projecting node that is roughly symmetrical in profile. Also, the venter of the petiole usually has a distinct sinuosity that often includes a small anteroventral process. A peculiarity I have noticed among worker specimens from Ari- zona is that they vary significantly in size, with some appearing to have allometrically enlarged heads.
Variant 1 ( Figure 93A-C) was collected in Sinaloa, Mexico. It is very similar to the type form except as follows: promesonotum more domed; pronotal dorsum strongly carinulate, without punctae.
Variant 2 ( Figure 93D-F) was collected from Volcán de Tequila in Jalisco, Mexico. It is similar to the type form except as follows: pronotum mostly smooth; petiolar node in profile broader; petiolar venter in profile straight, not sinuous.
Variant 3 ( Figure 93G-I) is from the drier portion of Oaxaca (Asunción Nochixtlan). It varies from the type form as follows: promesonotum distinctly domed and mostly smooth; petiolar node broader, more robust; face sculpture reduced, with posterior margin becoming smooth, and rugoreticulae less visible. Similar-looking specimens also occur in Mexico state (Temascaltepec).
Variant 4 ( Figure 93J-L) is from another site in Oaxaca (10.6km N Jct 190/135). It varies from the type as follows: promesonotum in profile low-domed and appearing very long, with the anterior face sloping gently into the metanotal groove; pronotum with many longitudinal carinulae around humeri, and a few on dorsum; gastral pilosity longer.
Variant 5 ( Figure 94A-C) is a wet forest version of S. huachucanum. It occurs at several sites on the eastern slope of the mountains in Querétaro. There are similar looking specimens from San Luis Potosí and Hidalgo states. It differs from the type population as follows: overal body size smaller; face sculpture reduced, with posterior ¼ or less of head smooth, remaining sculpture consisting of fine punctae, carinulae, and rugoreticulae; pronotum and dorsum of mesonotum smooth; promesonotum in profile variable, sometimes more flat, with posterior face merging smoothly into metanotum, sometimes more distinctly domed; petiolar node in profile narrow, appearing anteroposteriorly compressed. The specimens with a more domed promesonotum appear intermediate with variant 6.   Worker diagnosis. Integument mostly dark brown to brown; small-sized species (see HL, ML, PrW below); basal margin of mandible straight, never with a basal notch or depression; anterior clypeal margin with a shallow median emargination (best viewed from an anterodorsal angle); face completely sculptured, mostly rugoreticulate; mesosoma mostly sculptured, dorsum of promesonotum with dense longitudinal rugae; eye of moderate size (EL 0.10-0.12, , oval-shaped, with 5-7 ommatidia at greatest diameter; gastral pilosity relatively long, sparse, and mostly suberect, sometimes with a few underlying decumbent setae; petiole in profile appearing somewhat elongate; petiolar node reaching a distinct apex, which points vertically; propodeal spines tuberculate to short (PSL 0.07-0.12, PSI 1.2-2.1); frontal lobes of moderate width (FLD 0.14-0.16, FLI 24-27), not greatly obscuring torular lobes in full-face view. Small-sized species; general body color mostly dark brown to brown, with appendages brown to orange-brown, becoming lighter toward extremities; setae golden brown; mandible with 5-6 teeth, consisting of 3 distinct apical teeth, a basal tooth, and 1-2 smaller inner teeth/denticles, which are often worn and indistinct; basal margin of mandible straight, without basal notch or depression; mandible mostly smooth and shiny, with scattered piligerous punctae, and some striations around base and along lateral surface; anterior clypeal margin with a shallow median emargination (best viewed from anterodorsal angle); median lobe of clypeus with a pair of faint longitudinal carinulae that diverge toward anterior margin, apex of lobe with a short transverse carinula, remainder of clypeus mostly smooth; posterior extension of clypeus between antennal insertions of moderate width (PCW 0.02-0.03), sides subparallel to slightly hour-glass-shaped; frontal lobes of moderate width (FLD 0.14-0.16, FLI 24-27), not greatly obscuring torular lobes in full-face view; head roughly oval-shaped (CI 87-92), with posterior margin slightly depressed medially; eye of moderate size (EL 0.10-0.12, REL 18-21), oval-shaped, with 5-7 ommatidia at greatest diameter; face mostly rugoreticulate, with some longitudinal rugae along midline; scape of moderate length (SI 85-96), almost reaching posterior margin when laid back; scape surface smooth and shiny, with scattered piligerous punctae; flagellum with distinct 4-segmented antennal club; mesosoma almost completely sculptured except for a small patch of smooth cuticle on side of pronotum; dorsum of pronotum densely rugose (longitudinal orientation), transitioning to rugoreticulae on mesonotum; upper half of side of mesonotum rugose; mesopleuron mostly punctate, with some rugulae; side of propodeum rugulose-punctate; dorsum and declivity of propodeum with transverse carinulae; promesonotum in profile low-domed, slightly asymmetrical with apex shifted anterior of midpoint; metanotal groove of moderate width and depth; propodeal spines tuberculate to short (PSL 0.07-0.12, PSI 1.2-2.1); petiole appearing of moderate length to slightly elongate (PL/HW 0.47-0.54); petiolar node in profile of moderate height (PH/PL 0.55-0.66), and roughly symmetrical, dorsum pointing vertically to slightly posteriad, and usually reaching a well-defined apex; postpetiole in profile slightly asymmetrical, with anterior face longer and more sloping than posterior face, overal size similar to petiolar node (PPH/PH 0.85-0.98); anterior faces of petiolar and postpetiolar nodes mostly smooth and shiny, remaining surfaces faintly punctate; gaster smooth and shiny, with scattered piligerous punctae; most of body dorsum with short to long standing pilosity; setae on gastral dorsum relatively sparse, mostly long and suberect, with a few shorter decumbent setae underneath; setae on scape and legs decumbent to appressed, with some longer suberect setae on femoral venters and coxae.  Same as worker except for standard queen modifications and as follows: pronotum with transverse rugae/carinulae; mesoscutum densely longitudinally carinulae; scutellum rugose to rugoreticulate; propodeum with transverse carinulae that wrap around entire surface; mesopleuron mostly smooth; gastral pilosity denser, especially lower decumbent layer; wing as in Figure 98D.
Male. See Figure 98E-G. Biology. Stenamma ignotum is found in a diversity of wet forest habitats (e.g. cloud forest, mesophyll forest, wet oak forest) from 500 m to 2070 m elevation, but is most common above 1,000 m. Most collections are from sifted leaf litter taken from the forest floor, but it is also known from cookie baits and by general searching. A couple of nests have been found: one underneath a rock, and the other under epiphytes on the ground, both in montane wet forest. A single stray worker has been collected from a mud bank.
Comments. This species is very similar to S. crypticum, S. nonotch, and S. picopicucha, but should always be separable by its having the basal margin of the mandible straight and the anterior clypeal margin with a distinct median emargination. Some specimens of S. nonotch have a nearly imperceptible notch in the anterior clypeal margin, but this is always very insignificant compared to the emargination present in S. ignotum. Sculpture on the pronotal dorsum can be compared to confirm species status, with S. ignotum always having distinct longitudinal carinulae and S. nonotch having rugoreticulae or very irregular rugae. As described in the comments section of S. crypticum and S. picopicucha, the latter species is intermediate between S. crypticum and S. ignotum and it is unclear to which it is most closely related. There is a significant gap in distribution between S. ignotum and S. picopicucha, so I highly doubt that they are conspecific, but this has yet to be tested by including S. picopicucha in a molecular phylogeny.
There is some variation in size and sculpture among populations of S. ignotum, but the differences are minute. The only exception is a distinct variant (Figure 97) known from a single specimen from Guatemala (7.3km E Purulhá). This specimen has very long propodeal spines, and the dorsum of the petiolar node in profile reaches a rather sharp apex, which points distinctly posteriad. Until more specimens are found, I treat this variation as intraspecific. I have noticed that many species become more aberrant in the area near Purulhá, possibly because the area is very wet and cold.   margin with a single median emargination; frontal lobes somewhat narrow, not completely obscuring torular lobes in full-face view (FLD 0. ; propodeal spines present, forming short broad triangles (PSL 0.11-0.12, PSI 1.4-1.6); gastral pilosity short and clearly bilayered, with a layer of suberect setae and a layer of decumbent setae. Small-sized species; general body color a mottled pale yellow-brown with patches of darker brown, appendages similar; setae golden brown; mandible with 6 teeth, consisting of 2-3 distinct apical teeth, a basal tooth, and 2-3 middle teeth, which are usually worn and indistinct; basal margin of mandible straight to slightly sinuous, without a basal notch or deep depression; mandible mostly smooth and shiny, with scattered piligerous punctae; anterior clypeal margin with a median emargination, clypeus bordering emargination slightly projecting and attenuate, appearing translucent; median lobe of clypeus obliquely flattened, lacking longitudinal carinulae, apex near anterior clypeal margin with a short transverse carinula, remainder of clypeus smooth and shiny; posterior extension of clypeus between antennal insertions of moderate width (PCW 0.03-0.04), sides subparallel; frontal lobes somewhat narrow (FLD 0.15-0.16, FLI 25-28), with underlying torular lobes clearly visible in full-face view; head appearing subrectangular to oval-shaped (CI 83-87), posterior margin flat to very slightly depressed medially; eye relatively small (EL 0.06-0.08, REL 10-13), subcircular, with 3-5 ommatidia at greatest diameter; face completely covered with longitudinal rugulae and piligerous punctae, rugulae sometimes merging, but never becoming truly reticulate, posterior margin of head near occipital foramen mostly smooth and shiny; scape of moderate length (SI 92-98), not quite reaching posterior margin of head when laid back; scape surface mostly smooth and shiny, with scattered piligerous punctae and fine striations; flagellum with a somewhat distinct 4-segmented antennal club; mesosoma mostly with longitudinal carinulae and rugulae, some faint punctae also present on most surfaces (a few aberrant specimens with transverse carinulae on pronotum); propodeal dorsum and declivity with faint transverse carinulae; promesonotum in profile low-domed, roughly symmetrical; metanotal grove well demarcated, of moderate width and depth; propodeal spines present, forming short broad triangular projections (PSL 0.11-0.12, PSI 1.4-1.6); petiole in profile somewhat compact (PL/PW 51-55), node domed and pointing slightly posteriad, node dorsum flat to gently rounded; postpetiole somewhat dorsoventrally compressed, clearly smaller than petiolar node (PPH/PH 0.77-0.82); petiolar and postpetiolar nodes mostly smooth and shiny, re- maining waist surfaces faintly punctate; gaster mostly smooth and shiny, with scattered piligerous punctae; most of body with short standing pilosity; setae on scape decumbent to appressed; gastral pilosity short, somewhat dense, and clearly bilayered, with a layer of suberect setae and a layer of decumbent setae (setae on head similar); setae on legs mostly decumbent to appressed, with some suberect setae on venter of profemur. Same as worker except for standard queen modifications and as follows: body color a darker yellow-brown; pronotum with transverse carinulae on sides, smooth in middle; mesoscutum carinulate, with carinulae long and distinct; katepisternum mostly smooth; propodeum with transverse carinulae that wrap around surface; propodeal spines blunt, slightly longer.

Biology. Stenamma lagunum is known only from extractions of sifted leaf litter.
It is a high-elevation species, occurring from 1730-1900 m and is found in mesic forest habitats, such as oak-pine forest, oak forest, and montane scrub.
Comments. Stenamma lagunum is a very distinctive species that appears to be endemic to the mountains of southern Baja CA. It might be confused with its sister species S. excisum, but can be easily separated by its carinulate facial sculpture and more projecting median lobe of the clypeus. There is the chance that if S. lagunum occurs farther north in Baja CA, it might overlap with Holarctic Stenamma species, such as S. californicum. HOC species should be easy to separate out by their distinct clypeal carinae.  Worker diagnosis. Integument mostly dark brown to brown; medium-sized species (see HL, HW, ML below); lateral margin of hypostomal bridge with a projecting subquadrate to broadly-rounded lobe (usually visible behind mandible in profile); propodeal spines long and rather slender (PSL 00.17-0.22, PSI 1.9-2.2); anterior clypeal margin with a median emargination; basal margin of mandible straight, without a basal notch or depression; head and mesosoma densely carinulate; eye large (EL 0. , with 6-8 ommatidia at greatest diameter; petiolar node in profile subconical, with apex well-defined, almost sharp; postpetiolar node anteroposteriorly compressed; gastral pilosity with a layer of long suberect setae and a sparse layer of shorter decumbent setae; frontal lobes of moderate width (FLD 0.21-0.23, Medium-sized species; general body color dark brown to brown, with appendages brown to orange-brown; setae dark golden brown; mandible with 6 teeth, with two teeth nearest basal tooth smaller, often worn and indistinct; basal margin of mandible straight, without a basal notch or depression; mandible surface mostly smooth and shiny, with scattered piligerous punctae; anterior clypeal margin with a median emargination; median lobe of clypeus with a pair of faint longitudinal carinulae that diverge anteriorly, apex with a short transverse carinula, remainder of clypeus mostly smooth and shiny, with a few faint striae on median lobe; posterior extension of clypeus between antennal insertions of moderate to somewhat wide width (PCW 0.04-0.08); frontal lobes of moderate width (FLD 0.21-0.23, FLI 26-31), not completely obscuring torular lobes in full-face view; lateral margin of hypostomal bridge with a projecting subquadrate to broadly-rounded lobe that is usually visible behind mandible in profile, but some specimens with lobe reduced; head subcircular to oval-shaped (CI 87-96), posterior margin with a slight median depression; eye large (EL 0. , roughly oval-shaped, with 6-8 ommatidia at greatest diameter; face densely sculptured with a fan of longitudinal carinulae that extend outward from frontal lobes, lateral margins with shorter less densely spaced rugulae, interstices faintly punctate; scape of moderate length (SI 87-98), nearly reaching posterior margin of head when laid back; scape surface mostly smooth and shiny with scattered piligerous punctures; flagellum with a somewhat distinct 4-segmented antennal club; mesosoma densely sculptured; promesonotum mostly longitudinally carinulate, with some transverse carinulae wrapping around anterior declivity; mesopleuron and side of propodeum with irregular rugulae, rugoreticulae, and punctae; propodeal dorsum and part of declivity with transverse carinulae, remainder of declivity smooth and shining; promesonotum in profile low-domed and somewhat asymmetrical, with posterior slope longer and shallower than anterior slope; metanotal grove well demarcated and moderately deep, forming a rather smooth transition with promesonotum; anterior margin of propodeal dorsum in profile sometimes distinctly raised and separated from metanotal grove; propodeal spines long and rather slender (PSL 00.17-0.22, PSI 1.9-2.2), pointing anteroposteriorly and outward from body; petiole of moderate length (PL/HW 0.47-0.51), peduncle in profile somewhat slender; petiolar node in profile somewhat high (PH/PL 0.59-0.69), subconical and roughly symmetrical, with a well-defined apex that points vertically; postpetiolar node in profile usually somewhat anteroposteriorly compressed, with apex rounded and pointing vertically or slightly posteriad; anterior faces of petiolar and postpetiolar nodes smooth and shiny, posterior faces with punctae and a few rugulae, remaining surface of waist punctate; gaster mostly smooth and shiny, with scattered piligerous punctae and a few short striae around anterior constriction; most of body with rather long standing pilosity; scape with a uniform layer of subdecumbent to appressed setae; gaster with a layer of long suberect setae and a sparse layer of shorter decumbent setae; setae on legs mostly subdecumbent to appressed, with suberect setae on coxae and femoral venters.
Queen. Unknown. Male. Unknown. Biology. Stenamma leptospinum is known only from Winkler and Berlese samples of sifted leaf litter taken from the forest floor. It has been collected from 1650-2000 m elevation in montane wet forest habitats, including cloud forest and montane oak forest.
Comments. This species could be confused with S. longinoi, S. manni, or S. muralla, but it should be easy to distinguish by its dense carinulate sculpture and long, slender propodeal spines.
It is worth noting that the lateral hypostomal lobe that groups S. leptospinum with the other similar species is sometimes reduced, usually becoming shorter and only broadly rounded. When the lobe is reduced it can be more difficult to see in profile view, but it should still be visible from a lateroventral view. I have not seen any specimens where it is completely reduced to a point, as in most other species of Stenamma.
Material   Worker diagnosis. Integument black to brown-black; medium-sized species (see HL, ML, PrW below); anterior margin of clypeus with shallow median emargination; basal margin of mandible straight, without notch or substantial depression; head and mesosoma mostly smooth and shining; mesosoma compact, with promesonotum distinctly bulging; petiolar node robust, tall, and distinctly angled posteriad; propodeal spines forming short broad triangles (PSL 0.09-0.14, PSI 1.7-2.5); setae on gastral tergites sparse, long, and suberect; eye of moderate size (EL 0.11-0.15, REL 19-23), ovalshaped, with 6-8 ommatidia at greatest diameter; frontal lobes narrow, not obscuring torular lobe in full-face view (FLD 0.14-0.18, FLI 25-28). Medium-sized species; general body color black to red-or brown-black, with mandibles and appendages lighter, usually dark brown to yellow-brown; setae light brown; mandible with 6 teeth, consisting of 3 distinct apical teeth, a basal tooth, and 2 inner teeth, which are often worn and indistinct; basal margin of mandible relatively straight, without any notch or significant depression; dorsal surface of mandible mostly smooth and shining, with scattered piligerous punctae and a few short basal striae; median lobe of clypeus with pair of very faint vestigial carinulae that diverge toward anterior margin, apex with a short transverse carinula, remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between frontal lobes moderately broad (PCW 0.05-0.07), with subparallel to slightly diverging sides; frontal lobes narrow, not obscuring torular lobes in full-face view; head roughly oval-shaped (CI 92-96), but appearing somewhat tear drop-shaped because of the angled anterior margin of the clypeus and position of eyes; posterior margin of the head flat, never distinctly depressed medially; eye of moderate size , oval-shaped, with 6-8 ommatidia at greatest diameter; face almost completely smooth and shining, with scattered piligerous punctae and a few longitudinal carinulae on gena; scape short (SI 80-85), not reaching posterior margin of head when laid back; scape mostly smooth and shining, with scattered piligerous punctae, and sometimes a few fine striae; flagellum with a distinct 4-segmented antennal club; mesosoma usually mostly smooth and shiny, with some longitudinal carinae in metanotal groove, and a few scattered rugulae on propodeum, but some specimens with more developed sculpture on mesonotum, mesopleuron, and propodeum, consisting of faint carinulae and punctae; promesonotum domed and distinctly bulging upwards above head and propodeum; promesonotal suture usually completely effaced dorsally, but in a few specimens pronotum appears separated from mesonotum; metanotal groove distinct and of moderate depth; propodeal spines short, forming broad triangles (PSL 0.09-0.14, PSI 1.7-2.5); petiole of moderate length (PL/HW 0.52-0.62), node in profile robust and very tall (PH/PL 0.66-0.80), with anterior face longer and more sloping than posterior face, dorsum of node distinctly angled posteriad, and almost reaching a sharp apex; postpetiole in profile subcircular to oval-shaped, somewhat globular, always smaller than petiolar node (PPH/PH 0.70-0.84), dorsum usually with a somewhat distinct longitudinal median lobe; petiole and postpetiole mostly punctate, sometimes with faint rugulae, anterior faces of nodes smooth and shiny; gaster smooth and shiny except scattered piligerous punctae; most of body with moderately long, erect to subdecumbent setae; scapes with subdecumbent to decumbent setae; setae on legs mostly decumbent to appressed, with some suberect setae on femoral venters and coxae.

Male. Unknown.
Biology. Stenamma llama is a cloud forest specialist occurring from approximately 1100 m to 1600 m elevation. All specimens are known from sifted leaf litter collected from the forest floor, except for one, which was found at a cookie bait card. It is a rare species currently known from only one site in Oaxaca, Mexico, and one site in Guatemala. At the Guatemala site, out of 100 mini-Winkler and six maxi-Winkler samples, only six specimens were collected. The completely smooth and shiny integument of S. llama suggests that it nests in a relatively wet microhabitat.
Comments. With its mostly smooth sculpture and bulging promesonotum, S. llama is a very recognizable species. These characters, along with those in the key and diagnosis, should make it easy to separate from all other Stenamma species.
Stenamma    Worker diagnosis. Integument black to brown-black and shining; medium-sized species (see HL, ML, PrW below); anterior clypeal margin with shallow median emar-gination; basal margin of mandible relatively straight, without notch or substantial depression; face mostly smooth and shiny; mesosoma with coarse, rugose to rugoreticulate sculpture on most surfaces; promesonotum in profile distinctly asymmetrical, with anterior face gently rounded, dorsal surface flattened, and posterior face short, straight and forming a relatively sharp angle with dorsum; petiolar node, generally robust, and distinctly angled posteriad; postpetiolar node in profile with a longitudinal dorsal lobe that projects out posteriad over postpetiole; eye of moderate size (EL 0.11-0.14; REL 18-22), oval-shaped, with 7-8 ommatidia at greatest diameter; propodeal spines ranging from short tubercles to long spines (PSL 0.10-0.22, PSI 1.3-2.6); setae on gastral tergites relatively sparse, long, and mostly suberect; frontal lobes narrow, not obscuring torular lobe in full-face view (FLD 0. . Medium-sized species; general body color black to brown-or red-black, with mandibles and appendages lighter, usually dark brown to yellow-brown; setae golden; mandible with 6 teeth, consisting of 3 distinct apical teeth, a basal tooth, and 2 inner teeth, which are often worn and indistinct; basal margin of mandible relatively straight, without a notch or significant depression; dorsal surface of mandible mostly smooth and shiny, with scattered piligerous punctae and a few short basal striae; median lobe of clypeus with a pair of vestigial longitudinal carinulae that diverge toward the anterior margin, apex with a short transverse carinula, remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between frontal lobes moderately broad (PCW 0.03-0.05), with subparallel to slightly diverging sides; frontal lobes narrow (FLD 0. , not obscuring torular lobes in full-face view; head roughly oval-shaped (CI 89-95), but appearing somewhat tear drop-shaped because of the angled anterior margin of clypeus and position of eyes; posterior margin of head flat, never distinctly depressed medially; eye of moderate size (EL 0.11-0.14; REL 18-22), oval-shaped, with 7-8 ommatidia at greatest diameter; face almost completely smooth and shiny, with scattered piligerous punctae and few longitudinal carinulae on genae; scape moderately long (SI 85-92), nearly reaching posterior margin of head when laid back; scape surface largely smooth and shiny, with scattered piligerous punctae, and sometimes with a few faint striae; flagellum with distinct 4-segmented antennal club; mesosoma almost entirely with coarse rugae and rugoreticulae; rugae usually with a predominately longitudinal orientation, but in some specimens rugae on mesonotum have a transverse orientation; katepisternum, metapleuron, and lateral portion of pronotum,  forming a relatively sharp angle with dorsum; promesonotal suture indistinct, but usually discernable, especially when the orientation of the pronotal and mesonotal rugae differ; metanotal grove distinct and of moderate depth; propodeal spines present and often relatively long, but sometimes (usually specimens from lower elevations) becoming reduced to short tubercles (PSL 0.10-0.22, PSI 1.3-2.6); petiole in profile relatively long (PH/HW 0.58-0.65) and very distinctive, having a long peduncle and robust node, which is markedly angled posteriad; petiolar node in profile with long sloping anterior face that begins at about middle of peduncle, posterior face shorter, but usually at a similar angle, dorsum of node broadly rounded to subquadrate; postpetiole in profile asymmetrical, with a long sloping anterior face, and a short nearly vertical posterior face, dorsum with a distinct longitudinal lobe that projects out slightly posteriad over postpetiole, lobe in dorsal view attenuating posteriad, giving it a pinched-in appearance; petiole and postpetiole with variable amount of rugae and punctae; anterior faces of nodes mostly smooth and shiny with remaining surfaces punctatorugose; punctae most visible on ventral surfaces; posterior slope of petiolar node sometimes with a median keel; in a few aberrant populations the petiole and postpetiole lack rugae and are almost completely punctate; gaster smooth and shiny, with scattered piligerous punctae; most of body with sparse layer of moderately long standing seate; setae on scape mostly subdecumbent; setae on remaining appendages suberect to decumbent, with longer suberect setae on femoral venters and coxae. Same as worker except for standard queen modifications and as follows: lateral surfaces of pronotum transversely rugose to rugoreticulate, median area smooth and shiny; mesoscutum longitudinally carinate, with carinae fanning out from middle of anterior margin; mesopleuron mostly smooth and shiny; wing venation as in Figure 108D.
Male. See Figure 108E-G. Biology. This species is known only from Winkler or Berlese extractions of sifted leaf litter taken from montane, mesophyll forests. Nests have never been collected. It is likely a mid-elevation specialist given its occurrence between 860 to 1620 m.
At the El Cielo reserve in northern Mexico, I found a lone worker that looked like S. lobinodus foraging on a mud/clay bank bordering the main road (specimen viewed with a hand lens). Unfortunately the worker escaped and no nest was located. The presence of the worker on a mud bank suggests that S. lobinodus may nest in banks like the similar-looking S. diversum (see biology above for this species). Both species have almost the same sculpture, color and propodeal spines.
Comments. Stenamma lobinodus, S. llama and S. tiburon constitute the lobinodus species group. This group can be diagnosed by the following characters: postpetiole with a distinctive longitudinal dorsal lobe, which sometimes projects posteriad over postpetiole (lobe less discernable in S. llama); petiolar node well-developed, and pointing distinctly posteriad, node usually very large in S. llama and S. lobinodus. Stenamma lobinodus and S. tiburon also share the feature that the promesonotum in profile is asymmetrical, with a long, rounded anterior face, flat top, and short posterior face. Sister to the lobinodus group is S. pelophilum. This species does not have the characteristic lobe on the postpetiole that defines this group.
Stenamma lobinodus can be separated easily from S. diversum and S. tico by observing its asymmetrical promesonotum and dorsal postpetiolar lobe. Although it has never been collected in sympatry with either species, it may co-occur with S. diversum in Oaxaca, Mexico.
Stenamma lobinodus varies significantly across its range. Generally specimens at lower elevations (800-1100 m) are smaller and have shorter propodeal spines than specimens from higher sites. This gradation of sizes is very clear at the El Cielo reserve in Tamaulipas, Mexico, where I collected a series of Winkler samples from 860 to over 1600 m. The specimens from 1300 m and higher have substantially longer spines and more robust petioles. These larger specimens more closely match the ones from the populations in Querétaro.
The populations from Taman in San Luis Potosí and Mirador Grande in Oaxaca are particularly aberrant and I describe them here as variant 1 of S. lobinodus ( Figure  107). Variant 1 specimens are smaller and have the propodeal spines reduced to small tubercles. Also, the petiole and postpetiole lack distinct rugae and are instead covered in a dense network of foveolae and punctae. Specimens of both populations are from lower elevation (1000 m) and they most closely resemble the low elevation specimens from El Cielo. However, the latter specimens have better developed spines and the petiole and postpetiole are rugose.
I have decided not to split these variants into a separate species because of lack of sympatry between the two forms and the fact that substantial variation exists along elevational gradients and among sites. Also, the Mirador Grande site, which is where most of the aberrant specimens are from, is very far away from the remaining populations. With that said, there is some evidence to suggest that variant 1 does indeed represent a distinct species. First, there is one record of variant 1 from Taman in San Luis Potosí, which is very near the El Madroño site in Querétaro (< 30 km). Second, the intrapopulation variation at El Cielo is substantial, yet it does not encompass the morphology of the aberrant specimens, even at the same elevation. Lastly, preliminary molecular evidence shows that a specimen from Mirador Grande is as divergent from El Madroño and El Cielo specimens as some clearly distinct (and sympatric) sister species pairs. To solve this problem, more collecting should be done in the region of Taman and El Madroño in order to find an area of sympatry or to provide additional fresh specimens for molecular work.
Material  Type material. Holotype worker. MÉXICO: Chiapas, Custepec, 15.72212°N, 92.94428°W ±30m, 1680m, 19 May 2008  Worker diagnosis. Integument mostly dark brown to dark red-brown; large-sized species (see HL, ML, PrW below); lateral margin of hypostomal bridge with a projecting quadrate lobe (visible behind mandible in profile); gaster, and most dorsal surfaces, with a layer of thickened suberect to subdecumbent setae, gaster also with sparse layer of thinner appressed setae; mesosoma, waist, and head densely punctate (punctae fainter on head); head and mesosoma with fine rugulae and rugoreticulae, which on the mesosoma merge into the punctae, making them less obvious; eye relatively small (EL 0. , oval-shaped, with 6-7 ommatidia at greatest diameter; anterior clypeal margin with a shallow median emargination; basal margin of mandible straight to slightly sinuous, without a basal notch or depression; propodeal spines short  Large species; general body color dark brown (almost black) to dark red-brown, with appendages and some parts of the gaster lighter brown; setae a rich golden brown; mandible with 6 teeth, middle 2 teeth near basal tooth sometimes worn and indistinct; basal margin of mandible straight to slightly sinuous, without a basal notch or significant depression; mandible mostly smooth and shining with scattered piligerous punctae and striae; anterior clypeal margin with a median emargination; median lobe of clypeus with a pair of faint longitudinal carinulae that diverge anteriorly, area in between carinulae slightly depressed, apex of median lobe with a short transverse carinula, remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions of moderate width (PCW 0.05-0.08), sides slightly hourglass-shaped; frontal lobes narrow FLI 26), not obscuring torular lobes in full-face view; lateral margin of hypostomal bridge with a projecting quadrate lobe (visible behind mandible in profile); head robust, somewhat heart-shaped (CI 91-93), with posterior margin broadly depressed medially; eye relatively small compared to HW (REL [13][14][15], but appearing of moderate size (EL 0.13-0.16 ), with 6-7 ommatidia at greatest diameter, oval-shaped; face densely sculptured with longitudinal carinulae and rugulae, becoming rugoreticulae toward lateral margins, interstitial areas noticeably punctate; scape relatively short (SI 81-88), not reaching posterior margin of head when laid back; scape surface with scattered carinulae and faint piligerous punctae; flagellum with a somewhat indistinct 4-segmented antennal club; mesosoma densely punctate, and with fine rugulae that merge into surrounding punctae; rugulae on anterior half of pronotal dorsum transversely arcuate across surface; rugulae on remainder of promesonotal dorsum longitudinal in orientation; pronotal side completely punctate; rugulae on mesopleuron somewhat reticulate; part of propodeal dorsum and declivity with transverse carinulae; promesonotum in profile low-domed and asymmetrical, with apex occurring anterior of midpoint; metanotal grove somewhat indistinct with anterior margin merging smoothly with promesonotal declivity; propodeal spines well-developed, short (PSL 0.16-0.19, PSI 1.4-1.6); petiole of moderate length and robust (PL/HW 0.47-0.50), node of moderate height (PH/PL 0.62-0.65), broadly domed, and pointing slightly posteriad; postpetiole in profile nearly symmetrical, somewhat bulging, about as high as petiolar node (PPH/PH 0.90-0.96); petiole and postpetiole completely punctate and with a few rugulae on posterior sides of nodes; gaster mostly smooth and shiny, with scattered piligerous punctae; much of dorsal body surface with a layer of stout standing setae; setae on scape thin, dense, and decumbent (almost pubescent); gaster with a short layer of thickened suberect to subdecumbent setae and a very sparse layer of thinner appressed setae; setae on legs mostly appressed, with a few suberect setae on the coxae and femoral venters.

Male. Unknown.
Biology. This species is known from a single collection event made in mesophyll forest at 1680 m elevation. A few workers were found under epiphytes in a treefall. Over 100 leaf litter samples were collected from the same site and no additional specimens were retrieved. Consequently, this species is likely to be arboreal in its habits.
Comments. Stenamma longinoi is similar to S. leptospinum, S. manni, and S. muralla, mainly because all share the lateral hypostomal lobe. However, S. longinoi is very distinct and should be easily separated from these other species by its punctate sculpture and thickened setae. Given the diversity of S. manni variants (see S. manni below), I do find it possible that S. longinoi is an arboreal version of S. manni. However, molecular data place S. longinoi firmly outside of the clade that includes S. manni and variants of S. manni that are from all over Mexico and Central America (Branstetter unpublished data). Furthermore, S. longinoi was collected in sympatry with S. manni and no intermediates were found.
Material examined. Known only from the type locality.   Worker diagnosis. Note that this species is highly variable. See comments section below discussing population variants. Integument color variable; medium-to largesized species (see HL, ML, PrW below); lateral apex of hypostomal bridge projecting ventrally as a subquadrate to broadly rounded lobe, which is usually visible behind base of mandible in profile view (sometimes visible only in lateroventral view); propodeal spines tuberculate to short (PSL 0.09-0.19, PSI 1.0-1.6); basal margin of mandi- ble straight; anterior clypeal margin with a single median emargination; face usually completely sculptured, mostly rugoreticulate, with some longitudinal rugulae/carinulae along midline, but sometimes face mostly smooth, with only some longitudinal carinulae; mesosoma usually mostly sculptured with carinae, rugae, rugoreticulae, or punctae, only sometimes with pronotum mostly or completely smooth; eye of moderate size (EL 0.10-0.16 , , oval-shaped, with 5-8 ommatidia at greatest diameter; frontal lobes of moderate width ; first gastral sternite and tergite sometimes punctate. Similar species: Stenamma felixi, S. leptospinum, S. megamanni, S. muralla. Geographic range. Mexico to Nicaragua. Medium-to large-sized species; general body color highly variable, ranging from mostly black (type population), to red-brown, to brown, to yellow-brown, with appendages lighter, especially at joints and toward extremities, generally brown or orange-brown to yellow-brown; setae golden brown; mandible with 6-7 teeth (usually 6), consisting of 3 distinct apical teeth, a basal tooth, and 2-3 smaller teeth in between, which are often worn and indistinct; basal margin of mandible straight, without a basal notch or depression; mandible mostly smooth, with scattered piligerous punctae, and a variable number of longitudinal striations, mostly at base and on lateral surface; anterior clypeal margin with a shallow median emargination; median lobe of clypeus often with a pair of faint longitudinal carinulae (type population) that diverge toward anterior margin, but sometimes distinct carinulae replaced or hidden by a variable number of irregular striations, apex of lobe usually with a short transverse carinula, remainder of clypeus mostly smooth; posterior extension of clypeus between frontal lobes of moderate width (PCW 0.05-0.08), with sides subparallel; frontal lobes of moderate width , never greatly obscuring torular lobes in fullface view; lateral apex of hypostomal bridge projecting ventrally as a subquadrate to broadly rounded lobe, which is usually visible behind base of mandible in profile view (reduced in type population; sometimes visible only in lateroventral view); head usually roughly oval-shaped (type population), but sometimes slightly elongate, or more often broad, becoming slightly heart-shaped (CI 82-91), posterior margin slightly to distinctly depressed medially; eye of moderate size (EL 0.10-0.16 , , ovalshaped, with 5-8 ommatidia at greatest diameter; face usually completely sculptured, mostly rugoreticulate (rarely completely), with some longitudinal rugulae/carinulae along midline extending from frontal lobes to posterior margin, coarseness of sculpture variable (average in type population); face rarely mostly smooth, with only some longitudinal carinulae along midline and on gena; scape usually of moderate length (type population), but sometimes relatively long and slender (SI 88-109), scape when laid back reaching and often surpassing posterior margin of head; scape surface variable, usually with scattered piligerous punctae and some carinulae (type population), but sometimes scape more smooth with carinulae reduced, or scape more robust, with carinulae coarser; flagellum with distinct 4-segmented antennal club; mesosoma sculpture highly variable, usually completely sculptured, without large patches of smooth cuticle, but sometimes pronotum mostly to completely effaced; dorsum of promesonotum carinulate (type population), rugose, or rugoreticulate (often with punctae), almost always with longitudinal orientation (some aberrant specimens with transverse orientation); side of pronotum carinulate (type population), rugulose, or punctate; mesopleuron and side of propodeum punctate to rugulose-punctate, generally with more rugulae on the propodeum; dorsum and declivity of propodeum with transverse carinulae; promesonotum in profile low-domed, and usually slightly asymmetrical, with apex shifted anterior of midpoint, and anterior face steeper than posterior face (some populations roughly symmetrical); metanotal groove usually well-demarcated, width and depth variable (average in type population); propodeal spines tuberculate to short (PSL 0.09-0.19, PSI 1.0-1.6); petiole in profile appearing average (type population) to slightly elongate (PL/HW 0.48-0.62), with peduncle usually thick and robust; petiolar node in profile usually of moderate size (PH/PL 0.51-0.66), with a broadly rounded dorsum that points vertical to slightly posteriad, rarely pointing distinctly posteriad; node sometimes somewhat compressed anteroposteriorly; posterior margin of petiole in profile sometimes distinctly bent downwards, creating a slight concavity below node; postpetiolar node in profile similar in size to petiolar node (type population) or bulging (PPH/PH 0.79-1.05, PW/PPW 0.70-0.86), shape of node subcircular to asymmetrical (slightly asymmetrical in type population); petiole and postpetiole usually mostly punctate, with anterior faces of nodes variably smooth and shiny (type population), sometimes nodes with rugulae, or rarely rugoreticulae; gaster usually smooth and shiny, within scattered piligerous punctae, but sometimes (mostly northern populations in drier habitats) first gastral tergite and sternite lightly to strongly punctate; pilosity highly variable, pilosity on gastral dorsum usually clearly bilayered, with a layer of longer suberect setae, and a layer of shorter decumbent setae, but length and density of each layer variable, lower layer sometimes very dense (almost pubescent), or somewhat sparse and more subdecumbent, causing it to blend in with upper layer, rarely upper layer very long and more dense (type population average), gastral setae never greatly strongly thickened; setae on scapes uniformly suberect to subdecumbent, never with a separate layer of longer suberect setae; setae on legs decumbent to appressed, with longer suberect setae on femoral venters and coxae.

Stenamma manni
Queen description. (7 measured Same as worker except for standard queen modifications and as follows (comparing queen and worker of type population form only; queen from Rancho Somecla): pronotum with transverse carinulae; mesoscutum and scutellum longitudinally carinulate; propodeum with transverse carinulae that wrap around entire surface; katepisternum mostly smooth; lower layer of setae on gastral dorsum denser; wing venation as in Figure  113D (cell underneath stigma probably aberrant, not present in other S. manni queens).
Male. See Figure 113E-G. Note that the male is from the locality Omilteme in Guerrero, Mexico, not the type locality. Males show some variation across the range of the species. Biology. This species is one of the largest and most conspicuous species of Stenamma, which is probably why it was the first Middle American species to be described. As defined here, S. manni occurs from 1200-3700 m elevation, but it seems to be most common between 2000-2500 m. It occurs in wet montane forests like cloud forest, and drier, more seasonal habitats, such as oak woodland. Specimens have been collected in leaf litter samples, at bait cards, in Malaise traps, and by general searching. I have found nests in logs, in the leaf litter, under rocks, and in the ground. In Central America, S. manni is commonly found at the edge of cloud forest in logs and in the ground under logs. All Stenamma manni nests tend to be very large, with hundreds to perhaps over a thousand workers (a complete colony census has not been carried out). Nests usually have brood, alates, and a single egg-laying queen. Stenamma manni is one of the most common Stenamma species to be found at bait cards, suggesting that they are active epigeic foragers. All foragers I have observed have been solitary.
Comments. Stenamma manni should be separable from most similar species by the combination of presence of a lateral hypostomal lobe; presence of tuberculate to short propodeal spines; and large body size. However, it should be evident from the worker description above that S. manni, as circumscribed here, is highly variable, and thus difficult to characterize in a very satisfactory way. Indeed, the manni complex, with all of its different variants, is a taxonomic nightmare. Nearly every population has unique, often distinctive features, and there is no evidence of sympatry among forms. It is also common to have populations that are intermediate in phenotype between variants. Because of this diversity, I have united most forms, even if very distinct, into one polytypic species. I describe many variants below, providing distinguishing characters for each and approximate geographic ranges. This should help in identification of S. manni as I have defined it, and will provide guidelines for future work on the complex. One S. manni-like variant that I did recognize as a distinct species is S. megamanni. This species occurs from Chiapas, Mexico to Nicaragua and is sympatric with S. manni at many sites. However, it is a variable species and difficult to recognize from S. manni at a large geographic scale. Within the range where both species occur, I often find two forms in sympatry. What I am calling S. manni always has lighter body color (usually dark red-brown), a smaller eye (usually 5-6 ommatidia at greatest diameter), and a larger, more bulging postpetiole. Stenamma megamanni, in contrast, is always black, has a larger eye (8 or more ommatidia at greatest diameter), and usually has the postpetiole similar in size to the petiolar node. In addition, there seems to be some ecological separation between the species. Even though S. megamanni does occur at high elevation and in leaf litter, I commonly find it nesting at lower elevations in riparian areas. I have found nests both in clay banks and under rocks along streams. I have never found S. manni in these environments. It could be that S. megamanni is an ecomorph of S. manni, but I have found both species together in samples of leaf litter. Molecular phylogenetic data so far show that S. megamanni forms a clade nested within the larger S. manni complex. My current hypothesis is that S. manni and possibly S. megamanni, include more than one species, making it difficult to adequately separate each at a wide regional scale.
As a preface to describing each variant of S. manni, I have noticed several phenotypic trends within the complex that correlate with habitat. Populations from drier areas, especially those from central and western Mexico, tend to be lighter in color, have more developed sculpturing, and have denser pilosity, with the lower layer of gastral pilosity often pubescent. In contrast, specimens from wet forest environments are often shinier and less sculptured and have sparser pilosity. They also tend to be darker in color, but not always.
Characteristics of the type population ( Figure 110C, D, F) are indicated within the worker and queen descriptions (see parenthetical comments). It is important to note that although these specimens now appear brown in color, the original description says that they were black, with the tarsi, leg joints, and tips of the mandibles and antennae dark red. Overall, these specimens seem to be rather average looking in size, sculpture, and pilosity, compared with many other S. manni populations. Only the eyes seem somewhat large relative to head size. Most other S. manni populations have one or more characters exaggerated in some way. Another important observation is that these specimens were collected from between 3050-3350 m under a rock in pine forest. This is very high for tropical ants in general, and is one of the highest records for Stenamma. The only report of MAC Stenamma from a higher elevation is from 3700 m at the locality Rancho Somecla on Pico de Orizaba in Veracruz, Mexico. These specimens are also S. manni and they are the most similar in morphology to the type population. I should comment that in color and eye size, the type population might appear more similar to S. megamanni than some of the variants below. However, specimens from the type population are much smaller than S. megamanni and the sculpture and pilosity are different. Also, I see intermediate forms within Mexico that seem to connect the type population with the other variants.
Variant 1 ( Figure 110A, B, E, G, H, 111A-C) is the form that co-occurs with S. megamanni in Central America. It has been collected from Chiapas, Mexico, to Nicaragua, and as mentioned above, can be distinguished by its dark red-brown coloration, smaller eye, and bulging postpetiole, which is usually distinctly larger than the petiolar node in profile view. It occurs almost exclusively above 2000 m. Some populations (e.g. Huitepec) have extremely large workers with allometrically enlarged scapes and metafemurs. Compared to the type population, these larger specimens look like giants. Among populations of this variant within Central America, there is considerable sculpture and size variation.
Variant 2 ( Figure 111D-F) is known only from the Atlantic slope of the Sierra Juarez Mountains between Oaxaca and Valle Nacional in Oaxaca, Mexico. All collections were above 1650 m in cloud forest habitat. I tend to think of this variant as a high elevation, wet forest-adapted version of S. manni. Variant 2 is characterized by the following: general body color brown to yellow-brown, mottled; face mostly smooth and shining, with only some faint carinulae extending back from frontal lobes; pronotum almost completely smooth and shiny; scape slender, somewhat elongate (SI 102-106); metafemur relatively elongate (MFI 82-83); propodeal spines well developed, short (PSL 0.13-0.17, PSI 1.4-1.6); anterodorsal margin of propodeum forming a distinct welt, causing the metanotal groove to appear deep; petiolar and postpetiolar nodes somewhat compressed anteroposteriorly; postpetiolar node enlarged, somewhat bulging; gastral pilosity indistinctly bilayered, with lower subdecumbent layer of setae sparse. The gestalt of this variant is most similar to variant 1. Both have the postpetiole more bulging, and the scape and metafemur longer. The shape of the propodeum in profile is also very similar. Confirming the similarity, molecular phylogenetic data show variant 2 being more closely related to a specimen of variant 1 from Chiapas, Mexico, than to specimens further north in Mexico (Branstetter unpublished data). It is important to note that this variant occurs in sympatry with S. leptospinum. Intriguingly, both share the anteroposteriorly compressed petiolar and postpetiolar nodes.
Variant 3 ( Figure 111G-I) occurs at Nevado de Colima in Jalisco, Mexico, with similar forms at other nearby sites. It seems to be a version of S. manni that is adapted to drier habitats. It is characterized by the following: eye somewhat small, with 6 ommatidia at greatest diameter; dorsum of promesonotum rugoreticulate; side of mesosoma strongly punctate; petiole and postpetiole completely sculptured, mostly punctate, with rugoreticulae on dorsal surfaces of nodes; posterior portion of petiole bent downward, creating a small concavity under node; first gastral sternite strongly punctate; first gastral tergite punctate, but punctae broader, more like small dents, and less dense than sternal punctae; pilosity on gastral dorsum distinctly bilayered, with a layer of long suberect setae, and a layer of very dense (almost pubescent) decumbent setae, dorsum of petiolar and postpetiolar nodes with similar pilosity. There is some evidence for sympatry at Nevado de Colima. Variant 3 was collected at 2070 m. A few specimens of a similar S. manni form were collected at 2440 m (same label as variant 3, but different elevation). These specimens do not have distinct rugoreticulae and the dense pubescence, but seem otherwise similar. Because of the difference in elevation between the specimens, the paucity of material, and the existence of intermediate specimens at other sites, I do not consider this potential sympatry as sufficient evidence for calling variant 3 a new species. However, Nevado de Colima would be a good site to visit to further study species boundaries in this complex.
Variant 4 ( Figure 111J-L) is known only from Pinal de Amoles, Querétaro, Mexico and is similar to variant 3. It could be a mesic forest version of variant 3, as it occurs in wetter oak-pine forest on the Atlantic slope of the Sierra Gorda. It is characterized by the following: general body color dark red-brown to brown; head noticeably broad and thick; eye small, with 5-6 ommatidia at greatest diameter; dorsum of promesonotum rugoreticulate-punctate, but rugoreticulae poorly developed on middle of dorsum, strongest on humeri; side of mesosoma strongly punctate; propodeal spines well-developed, somewhat robust, and distinctively shaped, being broad at the base and then curving outward, appearing somewhat hook-like; petiole noticeably elongate and bent downward at posterior margin; petiolar node in profile broad and subconical, reaching a defined apex; petiole and postpetiole almost completely punctate; first gastral sternite and tergite lightly punctate; pilosity on gastral dorsum somewhat dense, and clearly bilayered, with a layer of longer suberect to subdecumbent setae, and a layer of decumbent setae, both layers similar in density. Specimens with intermediate morphology between variant 3 and 4 occur in Oaxaca on the western, drier side of the state. Among these specimens there is variation in the development of punctae and pubescence on the gaster, which seems to be clearly linked with elevation. One population from 2350 m (15.5km NE Oaxaca) has no punctae on the first gastral sternite and reduced gastral pilosity. In all other respects it is identical to populations from lower elevations within the state.
Variant 5 ( Figure 112A-C) is known from a single collection in Jalisco, Mexico. It is characterized by two main features: pronotal dorsum and face densely rugoreticulate; pilosity on most of dorsal surface of mesosoma, waist, and gaster very dense, long, and flexuous. This variant is probably most similar to variant 3.
Variant 6 ( Figure 112D-F) is known from several sites in Guatemala (Cerro Carmona, Salama, Guatemala City), and Honduras (PN Celaque), ranging from 1500-2000 m approximately. It has the following distinctive features: head oval-shaped, somewhat narrow; pronotal dorsum rugoreticulate; side of pronotum punctate; body in profile appearing somewhat elongate and gracile; petiole long and gracile, node asymmetrical, with a long sloping anterior face and a short posterior face, dorsum usually pointing distinctly posteriad; postpetiole somewhat smaller than petiolar node, not bulging. I suspect this variant could be a distinct species. It occurs in sympatry with variant 1 of S. manni at Cerro Carmona and has been collected near S. megamanni. However, it is very rare (only ten specimens known), and no nests or queens have been found. Molecular phylogenetic data infer it to be closely related to variant 1 and S. megamanni. More sampling is needed to test its status.
Variant 7 ( Figure 112G-I) is known only from RN Datanlí El Diablo in Nicaragua. It is similar to variant 6, except as follows: pronotal sculpture mostly longitudinally carinulate, with a patch of smooth cuticle in middle of dorsum; pilosity more dense; setae on legs noticeably thickened and subdecumbent (best observed in dorsal view).
Variant 8 ( Figure 112J-L) is known from two specimens collected at almost 3000 m at the Sendero Ecologico La Maceta locality in Guatemala. It has the following distinguishing features: eye large, with 9 ommatidia at greatest diameter; pronotum mostly smooth, with some transverse carinulae; postpetiole similar in size to petiolar node; gastral pilosity sparse, and weekly bilayered. This variant is most similar to the type population, in terms of sculpture, body and eye size. Unfortunately, neither specimens from the type population, nor this variant have been included in phylogenetic analyses, so it is unclear how they are related. A few faded specimens from Tajumulco, Guatemala look similar.   Worker diagnosis. Integument mostly black, or dark brown to brown; mediumsized species (see HL, ML, PrW below); basal margin of mandible usually sinuous, with a distinct basal depression, but without a basal tooth (rarely basal margin appearing nearly straight); anterior clypeal margin undulating, with 2 -4 distinct to somewhat blunt teeth; face sculpture variable, usually mostly smooth and shiny, with, at most, faint carinulae extending to about ¾ the distance to posterior margin of head, but some populations with face mostly rugoreticulate, with only area around posterior margin becoming smooth; pronotum sculpture variable, usually mostly smooth and shiny, but sometimes with some longitudinal rugulae on humeri, remainder of mesosoma with rugulae and punctae; postpetiole bulging, appearing distinctly larger than petiolar node (PPH/PH 0.96-1.14; PW/PPW 0.65-0.78); eye of moderate size , oval-shaped, with 6-8 ommatidia at greatest diameter (rarely 9 or 10); propodeal spines usually tuberculate, or at least forming a sharp angle, but sometimes forming a blunt angle, or becoming more developed, short (PSL 0.07-0.  Medium-sized species; general body color mostly black, or dark brown to brown, with appendages dark brown to orange-brown, lighter at joints and toward extremities; setae golden brown; mandible with 6-8 teeth (usually 7), consisting of 3 distinct apical teeth, a basal tooth, and 2-4 smaller teeth/denticles, which are often worn and indistinct; basal margin of mandible usually sinuous, with a distinct basal depression, but without a basal tooth, sometimes basal margin only slightly sinuous or nearly straight; mandible often mostly smooth and shiny, with scattered piligerous punctae and some striations (type population), but sometimes surface completely carinulate, with carinulae extending from base to near teeth; anterior clypeal margin forming 2-4 distinct to somewhat blunt teeth, outer teeth often larger and sharper than inner teeth (best viewed in anterodorsal view); median clypeal lobe with a pair of faint longitudinal carinulae, apex of lobe with a short transverse carinula, remainder of clypeus mostly smooth and shiny; area in between median lobe of clypeus and anterior clypeal margin forming a distinct cavity where mandibles insert; posterior extension of clypeus between antennal insertions of moderate width (PCW 0.02-0.0.05), with sides subparallel to slightly hour-glass-shaped; frontal lobes of moderate width , not greatly covering torular lobes in full-face view; head roughly oval-shaped (CI 83-93), with posterior margin flat to slightly depressed mesad; face sculpture variable, usually mostly smooth and shiny (type population), with, at most, faint carinulae extending to about ¾ the distance to posterior margin of head, but some populations with face mostly rugoreticulate, with only area around posterior margin becoming smooth; scape of moderate length (SI 80-101), reaching posterior margin of head when laid back; scape surface mostly smooth and shiny, with scattered piligerous punctae; flagellum with a distinct 4-segmented antennal club; pronotum and mesonotal dorsum sculpture variable, usually mostly smooth and shiny, but sometimes with longitudinal rugulae on humeri, remainder of mesosoma mostly sculptured (contrast between smooth pronotum, and sculptured mesonotum, mesopleuron, and propodeum distinctive); mesopleuron mostly punctate, with a few rugulae; side of propodeum with rugulae and some faint punctae; dorsum and declivity of propodeum with variable number of transverse carinulae; promesonotum in profile low-domed, and roughly symmetrical, but anterior declivity sometimes more sharply angled than posterior face (type population); metanotal groove in profile well-demarcated, anterior slope often smoothly transitioning with promesonotum; propodeal spines usually tuberculate (type population), or at least forming sharp angles, but sometimes forming blunt angles, or more developed and short (PSL 0.07-0.12, PSI 1.0-2.0); petiole of moderate length (PL/HW 0.46-0.56), with peduncle thick, often with anteroventral edge sharp; petiolar node in profile somewhat small (PH/PL 0.58-0.68), wedgeshaped, with anterior face longer and more sloping than almost vertical posterior face, dorsum of node rounded, and distinctly pointed posteriad; postpetiole bulging, globular, appearing distinctly larger than petiolar node (PPH/PH 0.96-1.14; PW/ PPW 0.65-0.78), anterior face of node much longer than posterior face; petiolar and postpetiolar nodes mostly smooth and shiny, remaining waist surfaces punctate, with a few rugulae around bases of nodes; gaster smooth and shiny, with scattered piligerous punctae; pilosity on face short, with a layer of sparse suberect setae, and a denser layer of decumbent setae, remainder of body dorsum with longer standing pilosity; pilosity on gastral dorsum usually distinctly bilayered, with a layer of longer suberect to subde- Same as worker except for standard queen modifications and as follows (comparison between worker and queen of type population form only): facial sculpture usually more developed (carinulae/rugulae longer and more distinct); mesopleuron mostly smooth and shiny; propodeum with transverse carinulae that wrap around entire surface; lower layer of gastral setae more dense, almost pubescent; propodeal spines (compared to worker from same population) slightly longer, more developed (PSL 0.13-0.17, PSI 1.4-1.7).
Male. Unknown. Biology. Stenamma maximon is an inhabitant of high elevation wet forest habitats (e.g. cloud forest, wet oak forest, hardwood forest, wet oak-pine forest), ranging from approximately 1700-2800 m elevation. When present, S. maximon workers are one of the most common components of the leaf-litter microenvironment, with most collections of the species made by sifting leaf litter from the forest floor. It has been collected also fairly commonly at cookie baits, suggesting that workers do forage epigeically some of the time. This is not surprising since S. maximon is a larger species of Stenamma. I have found only one nest of S. maximon, which was in a small log in leaf litter. A few stray workers have been collected also from underneath a rock. Given these observations, I would guess that S. maximon nests in wood in the leaf litter and forages both within the leaf litter and sometimes above it.
Comments. The presence of a bulging postpetiole, a sinuous basal margin of the mandible, and a toothed anterior clypeal margin, makes S. maximon easily separable from most other Stenamma species. However, S. maximon forms a complex of phenotypic variants (described below) and some populations lose the distinctiveness of the type population form and are more difficult to separate from similar species.
Distinctive features of the type population form (Figures 115, 116) are indicated in the species description (see parenthetical comments). Most notable are the characters mentioned in the previous paragraph, combined with a mostly smooth head and promesonotum. This form occurs mainly at high elevation sites in Chiapas, Mexico, and throughout most of Guatemala. It co-occurs with variant 1 at several sites in Guatemala.
Variant 1 ( Figure 116A-C) includes many populations in Guatemala and Honduras. Each is variable and some are intermediate in morphology between variant 1 and the type form. Variant 1 differs from the type form as follows: basal margin of mandible only slightly sinuous, without a distinct basal depression; teeth of anterior clypeal margin reduced, sometimes only two blunt middle teeth or undulations perceptible; face strongly sculptured with rugoreticulae and carinulae, only sometimes posterior ¼ of head smooth; lateral margins of promesonotal dorsum with distinctive oblique carinulae/rugulae that cross from upper portion of pronotal side to dorsum, middle of promesonotum smooth; propodeal spines reduced to blunt angles. I have found variant 1 with the type form most often at the locality 5km SE Antigua in Guatemala. Figure 116A-F shows two specimens from this locality, with D-F corresponding to the type form. This sympatry suggests that the two forms are somewhat reproductively isolated from one another. I have not separated variant 1 as a distinct species, however, because some populations, especially in Honduras, appear intermediate in phenotype. The general pattern I see is that the type form occurs in Chiapas, Mexico, to Guate- mala; variant 1 occurs in Guatemala, often in sympatry with the type form; and then populations in Honduras appear intermediate. I also see some similarity between variant 1 and certain populations of S. crypticum, perhaps indicating that these two species occasionally hybridize.
Variant 2 ( Figure 116G-I) is known from a few collections made from the wet side of the Sierra Juarez Mountains in Oaxaca, Mexico. These specimens are larger than average, have short propodeal spines (longer than in type form), and have lighter brown-black body coloration.
Variant 3 ( Figure 116J-L) is known from a single collection at 4.6km S Suchixtepec in Oaxaca, Mexico. It is similar to variant 2, except that the basal margin of the Worker diagnosis. Integument mostly black to red-black; medium-to large-sized species (see HL, ML, PrW below); lateral apex of hypostomal bridge projecting ventrally as a subquadrate to broadly rounded lobe, visible behind base of mandible in profile view; propodeal spines tuberculate (PSL 0.10-0.15, PSI 1.0-1.2); face and mesosoma usually completely sculptured with rugoreticulae and some carinulae (rarely with sculpture reduced); eye of moderate to large size (EL 0. , oval-shaped, with 8-11 ommatidia in greatest diameter; postpetiole usually appearing smaller than petiolar node (PPH/PH 0.85-0.98); basal margin of mandible straight to slightly sinuous; anterior clypeal margin with a median emargination. Medium-to large-sized species; general body color black to red-black, with appendages black or dark brown to orange-brown, becoming lighter toward extremities at joints; setae dark golden brown to golden brown; mandible with 6 teeth, 2 teeth nearest basal tooth sometimes worn and indistinct; basal margin of mandible straight to slightly sinuous, without a basal depression or notch; mandible mostly smooth, with scattered piligerous punctae and a few striations near base and on lateral surface; anterior clypeal margin with a simple median emargination; median lobe of clypeus usually with a pair of longitudinal carinulae (type population), but sometimes surface smooth, or with several irregular carinulae, area in between carinulae often de-pressed; apex of lobe usually with a single transverse short carinula (type population), but sometimes with several transverse carinulae/rugulae; remainder of clypeus smooth and shiny; posterior extension of clypeus between antennal insertions of moderate width (PCW 0.05-0.10), sides subparallel; frontal lobes of moderate width (FLD 0.22-0.29; FLI 25-28) not greatly obscuring torular lobes in full-face view; lateral margin of hypostomal bridge with a projecting subquadrate lobe, visible in profile view (very rarely reduced and only visible from a lateroventral view); head roughly oval-shaped to more robust, becoming strongly heart-shaped (CI 86-96), posterior margin of head with a distinct median depression (especially in larger specimens); eye moderately large (EL 0. , oval-shaped, with 8-11 ommatidia at greatest diameter; face sculpture variable, usually strongly rugoreticulate, with some carinulae along midline (type population), but sometimes sculpture more polished, with area near posterior margin of head becoming somewhat smooth; scape of moderate length (SI 89-100), reaching posterior margin of head when laid back; scape usually thick and robust, surface carinate to carinulae with piligerous punctae; flagellum with a somewhat indistinct 4-segmented antennal club; mesosoma sculpture variable, often densely rugose, with rugae wavy, almost becoming reticulate (type population), but sculpture often reduced, with promesonotum longitudinally carinulate to nearly smooth, and side of propodeum and mesopleuron more punctate; promesonotum in profile domed, and usually asymmetrical (type population), with apex shifted anterior of midpoint, but sometimes promesonotum symmetrical; metanotal groove welldemarcated, sometimes somewhat wide and with metanotum forming a small welt (type population); propodeal spines tuberculate (PSL 0.10-0.15, PSI 1.0-1.2); petiole of moderate length, usually somewhat robust (PL/HW 0.45-0.52); petiolar node in profile of moderate height (PH/PL 0.59-0.68), dorsum usually broadly rounded and pointing vertically, only rarely forming a sharp apex; postpetiole in profile usually appearing smaller than petiolar node (PPH/PH 0.85-0.98); petiole and postpetiole usually strongly punctate, with a few rugulae on dorsum and anterior face of postpetiolar node (type population), sometimes anterior faces of petiolar and petiolar nodes mostly smooth; gaster mostly smooth, with scattered piligerous punctae; most of body dorsum with relatively long standing pilosity; pilosity on gastral dorsum sparse and mostly suberect (type population), usually with some shorter subdecumbent setae, suberect setae often somewhat stout; setae on promesonotum often noticeably erect; setae on scape uniformly suberect to decumbent; setae on legs mostly decumbent to appressed, with some suberect setae on femoral venters and coxae.  Same as worker except for standard queen modifications and as follows: pronotum with transverse rugulae; mesoscutum longitudinally costulate; scutellum rugose to rugoreticulate; propodeum rugose to rugoreticulate; postpetiolar node larger, and somewhat anteroposteriorly compressed; mesopleuron mostly smooth; setae on mesoscutum short; setae on gastral dorsum often more dense, and more strongly bilayered, with layer of decumbent setae more dense; anterior quarter of gastral dorsum often with a layer of pubescence under stouter suberect and decumbent setae; wing venation as in Figure 121D.
Male. See Figure 121E-G. Note the rather peculiar propodeal protuberances. I have observed these in several specimens from different sites. Many males, however, including males from the same nest, have only small sharp tubercles.
Biology. Stenamma megamanni occurs from 700-2800 m, but it is most common from 1400-2000 m (there is also one dubious record from 150 m at Pico Bonito). It mainly inhabits montane wet forest environments, such as cloud forest, oak-pine forest, riparian forest, and mesophyll forest. Specimens have been collected in samples of sifted leaf litter, by baiting, by use of a Malaise trap, and by searching. Nests are known from rotting logs, under rocks, in mud and clay banks, and in dead bark. Most collections of this species have been inside closed-canopy forest, but it has been found several times nesting in clearings near cloud forest (similar to S. manni). The highest record of the species was a log nest in a clearing between lower elevation cloud forest and higher elevation pine forest.
The type population was found nesting under rocks along a stream in mesophyll forest. This population was rather intriguing, because the nests were common and foragers were very abundant. In fact, S. megamanni workers were more common at cookie bait cards placed along the stream than the usually more dominant ant genus Pheidole. This phenomenon of becoming locally abundant and dominant seems a frequent characteristic of this species. At Cerro Kilambé in Nicaragua, for example, S. megamanni was nesting in clay banks bordering a small stream and was the dominant ant in the area.
Nests of this species are large for Stenamma, often containing several hundred workers. One nest at Cerro Kilambé, which was excavated from a mud bank, had 2-3 nest entrances and many chambers all filled with brood. The nest went about 10 cm into the bank, contained about 250 workers and had abundant larvae and pupae. Another nest from the same site was similar in size, but the chambers were constructed around small roots. All excavated nests have had single dealate queens.
Comments. As described above under S. manni, separating S. megamanni from S. manni is difficult, because of the great diversity in S. manni phenotypes across its range. At a local scale, however, separating S. megamanni from S. manni is usually easy. Stenamma megamanni is black and has a rather large eye with 8 or more ommatidia at greatest diameter. Stenamma manni in contrast is usually a dark red-brown color and has a smaller eye with 5-6 ommatidia at greatest diameter. Preliminary phylogenetic data show that specimens from the type population and several divergent populations of S. megamanni form a clade nested within the S. manni complex (Branstetter unpublished data). This result has provided evidence that S. megamanni is a good species.
Within my concept of S. megamanni there is significant variation in sculpture, size and pilosity among populations. Because I perceive the variation to be somewhat continuous, I do not describe separate variants, but I do provide some images depicting the variation ( Figure 120A-F). The type form appears rather robust with the promesonotum high-domed, and asymmetrical, and the sculpture very dense ( Figure  119A-E). The pronotal sculpture has very wavy, almost reticulate rugae. Most populations do not match the type population exactly. The closest is a collection at the locality 2km NE Macalajau in Guatemala, which was made at high elevation (2320 m) from a ground nest under a rock in a cloud forest clearing. This habit is quite different from that of the type population, which was found at lower elevation along a stream (see the biology section above). More commonly, workers appear somewhat less robust ( Figure 120A-C), with less dense sculpturing. A few populations have workers with very reduced face and promesonotal sculpture, and with more erect pilosity ( Figure  120D-F). One aberrant high-elevation collection from Guatemala (Pinalón) has very large workers, with transverse carinulae on the pronotum ( Figure 120G Worker diagnosis. Integument mostly mottled brown to red-brown or orangebrown; medium-sized species (see HL, ML, PrW below); basal margin of mandible with a deep proximal notch containing a small tooth; anterior clypeal margin with a deep unevenly rounded depression that, when viewed from an anterodorsal angle, has two distinct outer teeth and two indistinct inner teeth (all pointing ventrally); mesosoma profile appearing elongate, almost gracile; metanotal grove relatively wide and shallow, not well demarcated by the promesonotal and propodeal margins; propodeal dorsum elongate, distinctly longer than propodeal declivity; gastral pilosity clearly bilayered, with a layer of long suberect setae and a layer of short subdecumbent setae; eye relatively small (EL 0.09-0.11, , with 5-6 ommatidia at greatest diameter; scape and metafemur relatively long (SI 104-120, MFI 70-80); frontal lobes well-developed , but not completely covering torular lobes in full-face view; 4-segmented antennal club very distinct. Similar species: Stenamma manni, S. saenzae.  (85), SI 104-120 (107), ,  , PSI 1.1-1.3 (1.3), MFI 70-80 (77), ACI1 62-64 (63), ACI2 93-98 (95).
Medium-sized species; general body color a mottled brown to red-brown or orange-brown, with patches of yellow-brown, especially on gaster; appendages generally lighter, orange-brown to yellow-brown; setae golden brown; mandible with 2-3 distinct apical teeth, 1-2 distinct basal teeth, and a variable number of almost imperceptible denticles in between (usually appearing as a long, flat diastema), basal tooth well-defined and robust; basal margin of mandible with a very deep proximal notch containing a small tooth; mandible mostly smooth and shiny, with scattered piligerous punctae and a variable number of striae; anterior clypeal margin with a deep unevenly rounded depression, that, when viewed anteriorly, has two distinct outer teeth and two indistinct inner teeth (all pointing ventrally); median lobe of clypeus somewhat obliquely flattened and concave, without a pair of longitudinal carinulae, only sometimes with a short transverse carinula before anterior margin, remainder of clypeus mostly smooth and shining; posterior extension of clypeus between antennal insertions somewhat narrow (PCW 0.03), sides subparallel; frontal lobes well-developed , but not completely covering torular lobes in full-face view; head elongate and roughly oval-shaped (CI 80-87), with posterior margin depressed medially; eye relatively small (EL 0.09-0.11, , subcircular to oval-shaped, with 5-6 ommatidia at greatest diameter; face densely rugoreticulate, with a few longitudinal rugulae medially, interstices with faint piligerous punctae; scape relatively long (SI 104-120), surpassing posterior margin of head when laid back; scape cuticle mostly smooth and shiny, with scattered piligerous punctae and fine striations; flagellum with a very distinct 4-segmented antennal club; mesosoma densely sculptured, promesonotal dorsum mostly with longitudinal rugae and rugoreticulae, but a few transverse rugulae present around anterior declivity; lateral side of mesosoma with irregular rugulae and punctae; propodeal declivity mostly smooth and shining, sometimes with faint transverse striae; promesonotum in profile low-domed and slightly asymmetrical, with the apex occurring anterior of the midpoint, anterior face more strongly defined and longer than posterior face; metanotal grove relatively wide and shallow, not well demarcated by the promesonotal and propodeal margins; propodeal dorsum elongate, distinctly longer than propodeal declivity; mesosomal outline in profile appearing elongate, almost gracile; propodeal spines forming sharp tubercles (PSL 0.12-0.15, PSI 1.1-1.3); petiole somewhat elongate and gracile (PL/HW 0.51-0.60), node small (PH/PL 0.53-0.56), with a long sloping anterior face, and a short vertical posterior face, dorsal surface in profile view rounded, pointing vertically; postpetiolar node slightly smaller than petiolar node (PPH/PH 0.90-0.97), anterior face longer and more sloping angled than posterior face; petiole and postpetiole mostly punctate, with anterior face of postpetiolar node largely smooth and shiny; gaster mostly smooth and shiny, with scattered piligerous punctae; much of body with long suberect to subdecumbent pilosity; scapes with mostly subdecumbent setae; gastral pilosity somewhat sparse and clearly bilayered, with a layer of long suberect setae and a layer of short subdecumbent setae; setae on legs mostly subdecumbent to appressed, with suberect setae on ventral surface of profemur.

Male. Unknown.
Biology. Stenamma monstrosum is a rare species known from only three collections of sifted leaf litter taken from the forest floor. It occurs in montane wet forest (e.g. cloud forest, mixed hardwood forest) and has been recorded from 1400-1650 m elevation. Because of its rarity in leaf litter, and its gracile phenotype, I hypothesize that S. monstrosum is arboreal.
Comments. Stenamma monstrosum looks like a cross between S. manni and S. saenzae. However, I doubt that a hybridization scenario is likely, because the species occurs at three different sites, and maintains a consistent phenotype among sites. It also is quite distinctive, with some of its own unique features, such as the shallow metanotal groove, and the deeply emarginate clypeus. These character states, along with the tooth in the basal margin of the mandible, will easily separate S. monstrosum from any other species.  Worker diagnosis. Integument mostly black or dark brown to brown; small-to medium-sized species (see HL, ML, PrW below); lateral margin of hypostomal bridge with a projecting subquadrate lobe, visible behind mandible in profile view; waist segments appearing somewhat slender, with postpetiole particularly small; eye relatively large (EL 0. , with 6-9 ommatidia at greatest diameter; anterior clypeal margin with a median emargination; basal margin of mandible straight; propodeal spines tuberculate (PSL 0.08-0.11, PSI 1.1-1.4); frontal lobes well-developed, but not completely covering torular lobes in full-face view ; head densely sculptured with carinulae, rugoreticulae, and faint punctae; mesosoma mostly sculptured, but pronotal sculpture variably effaced, sometimes mostly smooth and shiny; gastral setae mostly suberect, long, and relatively sparse. Small-to medium-sized species; general body color black or dark brown to brown, with appendages brown to yellow-brown; setae golden brown; mandible with 6 teeth, but two teeth nearest the basal tooth smaller, often worn and indistinct or denticulate; basal margin of mandible straight, without basal notch or depression; mandible surface mostly smooth and shiny, with scattered piligerous punctae and basal striae; anterior clypeal margin with a median emargination; median lobe of clypeus with a few faint punctae, but lacking longitudinal carinulae, apex with a faint transverse carinula; remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions of moderate width (PCW 0.03-0.06), sides subparallel; frontal lobes well-developed (FLD 0.16-0.19, FLI 24-28), but not completely obscuring torular lobes in full-face view; frontal carinae weak, fading into facial sculpture beyond frontal lobes, not surpassing level of anterior margin of eye; head oval-shaped (CI 87-90), posterior margin slightly depressed medially; eye relatively large (EL 0. , oval-shaped, with 6-9 ommatidia at greatest diameter; face densely sculptured with longitudinal carinulae along midline, turning into rugulae and rugoreticulae toward lateral margins, interstices punctate; scape of moderate length (SI 88-95), nearly reaching posterior margin of head when laid back; scape surface with a variable amount of fine punctae and striae; flagellum with distinct 4-segmented antennal club; pronotal sculpture mostly smooth and shiny, or with dense longitudinal rugulae and faint punctae, or with intermediate states with rugulae somewhat effaced (especially on pronotal side); mesonotal dorsum with fine carinulae and punctae; mesopleuron mostly punctate, with a few rugulae; propodeal side with rugulae and some punctae; propodeal dorsum and declivity with transverse carinulae; promesonotum in profile usually low-domed and roughly symmetrical, some specimens with promesonotum more robust, higher; metanotal grove well demarcated, of moderate depth and width; propodeal spines present as small tubercles (PSL 0.08-0.11, PSI 1.1-1.4); petiole and postpetiole appearing somewhat delicate with nodes relatively small (PL/HW 0.48-0.57, PH/PL 0.56-0.63, PPH/PH 0.74-0.84); petiolar node in profile pointing posteriad, with dorsum gently rounded; ventral surface of node concave; postpetiole in profile with a long shield-like anterior face and a short vertical posterior face, anterior half constricted; anterior faces of petiolar and postpetiolar nodes usually mostly smooth and shiny, remaining surface of waist segments mostly punctate; gaster mostly smooth and shiny, with scattered piligerous punctae and a few short striae around anterior constriction; most of body dorsum with moderately long standing pilosity; setae on scape suberect to appressed; gastral setae mostly suberect, long, and relatively sparse, a few shorter decumbent setae also present; setae on legs mostly subdecumbent to appressed, with suberect setae on coxae and femoral venters. Same as worker except for standard queen modifications and as follows: pronotum transversely carinulate/rugulose; mesoscutum and scutellum densely carinulate; mesopleuron mostly smooth and shiny; propodeum transversely carinulate, with carinulae wrapping around entire surface; petiole and postpetiole slightly more robust, with dorsum of petiolar node reaching a slightly more defined apex; gastral pilosity more dense.
Male. Unknown. Biology. Stenamma muralla occurs in montane wet forest habitats (e.g. cloud forest, mixed hardwood forest, pine-mesophyll forest, ridgetop cloud forest, riparian cloud forest) from 1100-1900 m. It has been collected in extracts of sifted leaf litter, at cookie baits, beating vegetation, and in a flight intercept trap (single worker). Nests have been found by general searching in a variety of microhabitats, including wet clay banks along streams, dry clay banks along road cuts (in forest), in dead wood, in the base of a tree fern, and in mud at the base of a fallen tree. Nests are of moderate size and usually contain a few chambers.
Comments. Stenamma muralla is similar to S. leptospinum, S. longinoi, and S. manni, because all have the lateral margin of the hypostomal bridge enlarged into a subquadrate lobe. However, S. muralla is easy to identify by its smaller size, more slender waist segments, and largely effaced pronotal sculpture. A few other species might look superficially like S. muralla, but these will not have the enlarged hypostomal lobe.
An interesting phenomenon in S. muralla is the regular occurrence of workers that are distinctly larger, and have the pronotum more densely sculptured with longitudinal rugulae/carinulae. Interestingly, the size difference seems to be discrete, rather than continuous. These specimens have been found in leaf litter samples as well as in nests, so they must be conspecific. They could be workers with queen-like traits (queens are larger than standard workers), but other than size and sculpture there are no further indications that they are intercastes. Another hypothesis is that they are a soldier-like worker caste. However, they do not show any allometric size differences. Small-sized species; general body color dark red-brown to brown, with appendages lighter, brown to yellow-brown toward extremities; setae golden brown; mandible with 6 teeth, basal tooth often well-defined, projecting; basal margin of mandible sinuous, with a distinct basal notch and accompanying small tooth; mandible mostly smooth, except for scattered piligerous punctae, and some striae around the basal and along lateral surface; anterior clypeal margin in anterodorsal view undulating, forming 4 blunt teeth (only outer teeth visible in full-face view); median lobe of clypeus with a pair of somewhat distinct longitudinal carinulae, that diverge toward anterior margin, apex of lobe with a short transverse carinula, remainder of clypeus mostly smooth; posterior extension of clypeus between antennal insertions somewhat narrow (FLD 0.14-0.16, FLI 28-31), with sides diverging slightly posteriad; frontal lobes somewhat expanded (FLD 0.14-0.16, FLI 28-31), but not completely obscuring torular lobes in full-face view; head roughly oval-shaped (CI 87-92), with posterior margin distinctly depressed medially; eye of small to moderate size (EL 0.08-0.10, , ovalshaped, with 4-5 ommatidia at greatest diameter; face mostly strongly rugoreticulate, with a few longitudinal carinulae along midline near frontal lobes; scape of moderate length (SI 90-99), not quite reaching posterior margin when laid back; scape surface mostly smooth, with faint striations and piligerous punctae; flagellum with a distinct 4-segmented antennal club; dorsum of pronotum with irregular longitudinal rugulae that sometimes merge, dorsum of metanotum more rugoreticulate-punctate, side of pronotum mostly carinulate, with a small patch of smooth cuticle near ventral margin, mesopleuron and side of propodeum rugulose-punctate, propodeal dorsum and upper half of declivity with transverse carinulae; promesonotum in profile low-domed, roughly symmetrical, but anterior face distinctly longer than posterior face; metanotal groove of moderate depth and width, sometimes with a small central welt (metanotum); propodeal spines tuberculate (PSL 0.07-0.09, PSI 1.2-1.4); petiole in profile of moderate length (PL/HW 0.48-0.54), peduncle somewhat slender, narrowing toward body; petiolar node of moderate height (PH/PL 0.52-0.61), asymmetrical, with anterior face slightly longer and more sloping than posterior face, dorsum of node narrowly rounded, almost becoming a well-defined apex, node always pointing distinctly posteriad; postpetiole in profile subspherical to oblong, appearing somewhat compressed anteroposteriorly, roughly symmetrical, and similar in size to slightly smaller than petiolar node (PPH/PH 0.83-0.99); anterior faces of petiolar and postpetiolar nodes mostly smooth, remaining surfaces mostly punctate, with some rugulae on posterior half of postpetiole; gaster mostly smooth and shiny, with scattered piligerous punctae; face pilosity short, bilayered; dorsum of mesosoma and gaster mostly with a sparse layer of thickened, suberect setae, gaster with a few thin decumbent setae; setae on scapes and legs mostly appressed, with some suberect setae on femoral venters and coxae.  12-0.15 (0.15), PPL 0. 14-0.15 (0.15), PPH 0. 14-0.17 (0.17), PPW 0. 15-0.18 (0.18) Same as worker except for standard queen modifications and as follows: pronotum transversely carinulate, with dorsum of cervical shield punctate; mesoscutum longitudinally rugulose, with some irregular reticulations; scutellum longitudinally rugulose to rugoreticulate, usually with a small patch of smooth cuticle mesad; propodeum with transverse carinulae that wrap around surface; mesopleuron mostly smooth; pilosity on gaster distinctly bilayered, with a stout layer of long suberect to subdecumbent setae, and a very dense layer of decumbent to appressed pubescence; wing venation as in Figure 129D.
Same as worker except for standard queen modifications and as follows: side of pronotum rugoreticulate to transversely rugose, center of pronotum transversely carinulate; mesoscutum mostly foveolate to longitudinally rugose, usually with some smooth cuticle along midline, foveolae when present piligerous; propodeum with transverse carinulae that wrap around surface; mesopleuron mostly smooth; pilosity on gastral tergites distinctly bilayered, with a sparse layer of longer suberect to subdecumbent setae and a dense layer of decumbent setae, lower layer usually almost pubescent, but sometimes less dense and longer; wing venation as in Figure 133D.
Male. Unknown. Biology. This species is known only from extracts of sifted leaf litter collected from the forest floor. It occupies a variety of wet forest habitat types (e.g. rainforest, mesophyll forest, 2° wet forest, Liquidambar forest, cloud forest, oak-pine forest) and occurs from near sea level to 2000 m. Dealate queens are commonly collected in samples, suggesting that the species may nest in the leaf litter microenvironment.
Comments. Stenamma nonotch forms a clade with S. nanozoi, S. sandinista, and S. schmidti and is very similar to these species (Branstetter unpublished data). However, it is the only species within the clade to have the anterior clypeal margin entire, and the basal margin of the mandible straight. This feature makes it easy to distinguish from its close relatives. Stenamma nonotch is also similar to S. ignotum and S. picopicucha, which both have a straight basal margin of the mandible. However, neither of these species have the anterior clypeal margin entire.
There is some variation among populations of S. nonotch, with workers differing in size, sculpture, and shape of the propodeal spines and petiolar node. I split this diversity into three variant forms. The type form ( Figure 131) includes all of the collections from Oaxaca, Mexico, which were collected below 700 m on the wetter side of the state. Variant 1 ( Figure 132A-C) occurs at the low-elevation locality Salto de Agua in Chiapas, Mexico. Compared to the type population, specimens are smaller, have a lighter red-brown coloration, have the propodeal spines slightly more robust and projecting dorsally, and have the petiolar node in profile somewhat anteroposteriorly compressed. Variant 2 ( Figure 132A-C) occurs at the mid-elevation locality Nahá in Chiapas, Mexico. It is smaller than the type form and has the propodeal spines noticeably reduced to sharp angles, rather than sharp, projecting tubercles. Lastly, variant 3 ( Figure 132D-F) is a high elevation version of S. nonotch, occurring mainly at the locality Coapilla in Chiapas, Mexico. Compared with the type form, it is larger, has darker coloration, and has a thicker petiolar node. Also, the ventral margin of the petiolar node is flat, rather than with a small concavity. Molecular data suggest that there is significant divergence among populations, but I have not seen sympatry among forms, and some populations have intermediate phenotypes. Thus, I treat the above as intraspecific variants until more data are available.
Male. Unknown. Biology. Stenamma ochrocnemis is known mostly from extracts of sifted leaf litter collected from the forest floor, but workers also have been found at cookie baits and once underneath a rock. The species is a high-elevation specialist occurring from approximately 1600-2750 m, with most collections around 2000 m. It inhabits wet montane forests, such as cloud forest, oak forest, hardwood forest, and mixed oak cloud forest.
Comments. The most distinctive feature of this species is its light colored legs, which always make it stand out from other Stenamma species when sorting specimens in ethanol. Stenamma ochrocnemis appears superficially similar to several other MAC species, but it should be separable by the characters listed in the diagnosis. Phylogenetic data show that S. ochrocnemis belongs to a clade that includes S. hojarasca and most likely S. cusuco (Branstetter unpublished data).
Across its range there is significant variation in body size, surface sculpture, gastral pilosity and the configuration of the clypeus and basal margin of the mandible. I describe several variants here, but it should be noted that almost every population has some distinctive feature, making separation of this species into discrete forms somewhat arbitrary. In the type population (Figure 135), the body has a very dark redbrown color, the pronotum is strongly rugose, the basal margin of the mandible has a large deep depression, and the anterior clypeal margin forms several sharp teeth. This form is rather distinctive and seems to be restricted to localities in Honduras.
Variant 1 ( Figure 135A-C) differs from the type population in that it has the pronotum mostly to completely smooth and shiny, it has lighter body color, and the depression in the basal margin of the mandible is not as deep. This form occurs mainly in Chiapas, Mexico, and Guatemala. Variant 2 ( Figure 135D-F) is a slightly different version of variant 1 and it is known from the locality Huitepec in Chiapas, Mexico. Workers are noticeably larger, the propodeal spines are more developed, and the petiole appears elongate, with the node in profile more asymmetrical.
Variant 3 ( Figure 135G-I) occurs mainly at the locality 5km SE Antigua in Guatemala, with similar forms at nearby sites. It has the pronotum mostly sculptured, it has lighter orange-brown body color, and it has the basal margin of the mandible only slightly sinuous, almost without a basal depression. Interestingly, this variant co-occurs with variant 1-like specimens ( Figure 135J-L) at the Antigua site, suggesting that there may be reproductive isolation between the two forms. I have noticed some ecological differences, with the more sculptured form occurring at slightly lower elevation and in more disturbed habitat than the less sculptured form. Molecular data, however, suggest there is only one species. I have sampled one specimen of each form from the Antigua site, and these are inferred to be sister to each other and nested within the larger S. ochrocnemis complex. This result shows that the specimens they are not grouping by sculpture type, but by locality. Additional evidence indicating the existence of only one species is that, specimens with intermediate phenotypes occur at other sites in Guatemala. Thus, I treat this variation as intraspecific.
Variant 4 ( Figure 135M-O) is known only from a few specimens collected at Cusuco in Honduras. It is similar to variant 1, except that it has the frontal lobes somewhat dorsolaterally expanded. The form of the frontal lobes is very similar to S. cusuco or S. hojarasca, which both occur at Cusuco and have strongly expanded frontal lobes. This similarity is either an indication of a shared selection pressure, or perhaps some level of hybridization among species.
I include the specimens from Guerrero, Mexico, in S. ochrocnemis with uncertainty. They represent the only collection of the species north of Chiapas, Mexico. Superficially they appear like variant 1, but there are some differences in sculpture and petiole shape, and it is difficult to interpret body and leg color because the specimens are old and faded. Until more material can be collected, I treat this record as dubious. CASENT0623451], [1w, UNAM, CASENT0623453], [1dq, 2w, USNM, CASENT0622334, CASENT0623455 [1w, UVGC, CASENT0623454].
Worker diagnosis. Integument mostly black to brown-black and shining; small to medium-sized species (see HL, ML, PrW below); anterior margin of clypeus with a shallow median emargination; basal margin of mandible straight to slightly curving, but without a distinct basal notch or depression; head and body almost entirely smooth and shiny, except for faint punctae on waist and sometimes on propodeum; pronotum in profile usually distinctly asymmetrical, with a long, steep posterior face, that forms a distinct angle with dorsal surface, and a short anterior face; eye of moderate size , oval-shaped, with 6-8 ommatidia at greatest diameter; propodeal spines reduced to small tubercles or short points (PSL 0.06-0.10, PSI 1.1-1.7); setae on gastral tergites sparse, moderately long, and mostly suberect; frontal lobes narrow , not obscuring torular lobe in fullface view. Small-to medium-sized species; general body color black to brown-black, with mandibles and appendages brown to yellow-brown, lighter toward extremities; setae translucent brown; mandible with 4-6 teeth, consisting of 3 distinct apical teeth, a basal tooth, and 2 inner teeth, which are very often effaced; masticatory margin of mandible sometimes gently curving inward (perhaps due to wear), causing basal tooth to appear more robust; basal margin of mandible straight to slightly curving, without a distinct notch or depression; some specimens with basal section of mandible, where mandible inserts under clypeus, distinctly expanded and thin; dorsal surface of mandible mostly smooth and shining, with scattered piligerous punctae and a few basal striae; median lobe of clypeus somewhat obliquely flattened, and sometimes angled more ventrally than average, creating distinct dorsal and anterior faces; median lobe with faint to absent longitudinal carinulae, middle of lobe often slightly concave, apex of lobe with a short transverse carinula, usually present near anterior margin, remainder of clypeus mostly smooth and shining; posterior extension of clypeus between frontal lobes of moderate width (PCW 0.03-0.05), with subparallel sides; frontal lobes very narrow , not obscuring torular lobes in full-face view; head somewhat longer than broad , roughly oval-shaped, posterior margin flat, never strongly depressed medially, lateral corners gently curving; eyes of moderate size , oval-shaped, with 6-8 ommatidia at greatest diameter; face almost entirely smooth and shiny, except for a variable number of carinulae around frontal carinae and on genae; scape of moderate to somewhat long length (SI 89-107), just reaching or slightly surpassing posterior margin of head when laid back; dorsal surface of scape with scattered piligerous punctae and a few faint striae, otherwise smooth and shining; funiculus with distinct 4-segmented antennal club; mesosoma usually almost entirely smooth and shiny, except for some longitudinal carinulae along metanotal groove, and transverse carinulae on dorsal and declivitous faces of propodeum; in some populations propodeum with more developed rugulae and punctae; promesonotum in profile usually asymmetrically domed and somewhat bulging, with posterior slope distinctly longer and straighter than anterior slope, and forming a more well-defined angle with dorsal surface, apex of promesonotum offset toward posterior margin; lateral and posterior margins of promesonotum in dorsal view, usually well defined, with relatively sharp transitions; one population (from high-elevation) with promesonotum in profile low-domed and roughly symmetrical; propodeal spines forming tubercles, or small projecting points (PSL 0.06-0.10, PSI 1.1-1.7); petiole of moderate length (PL/HW 0.51-0.58), node of variable height (PH/PL 0.59-0.69) and volume, usually pointing slightly posteriad, anterior face longer than posterior face and rising from about midpoint of petiole, posterior face nearly vertical, dorsum in profile usually narrowly rounded, but sometimes forming a defined apex; postpetiole in profile slightly to distinctly smaller than petiolar node (PPH/PH 0.76-0.89), roughly symmetrical, with anterior face slightly longer and more sloping than posterior face; petiole mostly smooth and shining, except for light punctae on venter and lateral portions of peduncle; postpetiole with anterior face smooth, shiny and shield-like, venter and posterior half of postpetiole lightly punctate; gaster mostly smooth and shiny, with scattered piligerous punctae; most of body with a thin layer of moderately long standing setae; setae on gastral tergites sparse and uniformly suberect; facial setae mostly decumbent with a few erect hairs; setae on scape subdecumbent to appressed; setae on legs mostly decumbent to appressed, with coxae and ventral surfaces of the femora with some suberect setae.  , PPH 0. 19-0.20 (0.20), PPW 0. , , FLI 24-26 (26), PSI 1.1-1.7 (1.2), , ACI1 65-67 (65), .
Same as worker except for standard queen modifications and as follows: scutellum with irregular longitudinal rugulae/carinulae; metapleuron with longitudinal carinulae; dorsum of propodeum with transverse carinulae; petiolar node usually same as in workers, but one queen (Huejutla population) with node dorsum in posterior/anterior view forming two sharp points, separated by a steep concavity.
Male. Unknown. Biology. This is a rare species that inhabits montane wet forests from 1000 to 1800 m elevation. Most collections are from Winkler or Berlese extracts of sifted leaf litter. However, at Cusuco National Park in Honduras, I found two nests in a mud bank bordering a stream. The surface of the bank was rocky with an overlying layer of dense mud. The first nest was located by haphazardly cutting into the bank in an area  where I saw lots of worker activity. This nest had a single chamber with about 35 workers and some brood. The second nest was located by following a returning forager. This nest had a nearly undetectable entrance (2 mm diameter) consisting only of a small hole, without any surrounding structure or excavated substrate. Behind the entrance was a very short tunnel leading to a single, small chamber. This contained 46 workers, some brood and a single dealate queen. When the nest chamber was disturbed, the queen immediately absconded out onto the clay bank followed by a series of workers carrying brood. Before excavation, foragers outside the nest were observed to be slow moving and solitary, similar to behavior in most other Stenamma species.
Comments. Molecular phylogenetic data show that Stenamma pelophilum is sister to the lobinodus species group, which includes S. llama, S. lobinodus, and S. tiburon (Branstetter unpublished data). Although S. pelophilum does not have the distinguishing features of this group, it does bear some similarity to S. llama and S. tiburon. It can be easily separated from these species by its distinctive promesonotum shape and average looking postpetiole, which lacks a distinctive dorsal lobe.
There is minimal morphological variation amongst most populations of S. pelophilum, and I interpret this variation to be intraspecific. One population, however, is significantly divergent from the type population and I describe it here as variant 1 ( Figure 139A-C). This variant is known from above 2000 m in Oaxaca, Mexico, on the wet, eastern slope of the Sierra Juarez. It is larger, has more sculpture on the mesopleuron and propodeum, and has the promesonotum in profile low-domed and roughly symmetrical. Also, it has a relatively longer scape and metafemur than other populations of standard S. pelophilum (SI ≥ 100 vs. ≤ 96, MFI ≤ 86 vs. ≥ 93). It could be that this variant is a mountaintop endemic, derived from the S. pelophilum populations found lower on the mountain. I choose, however, to include variant 1 within S. pelophilum, because I have found specimens with intermediate phenotypes ( Figure  139D-F). These have been collected from intermediate elevations, and from the same samples as variant 1. The morphological differences might be due to environmental effects on development, rather than reproductive isolation and divergence. It would be interesting to investigate the population dynamics between these two forms along the elevational gradient.
Male. Unknown. Biology. Stenamma picopicucha occurs from 1400-2300 m elevation, and is a specialist of montane wet forest habitats, such as cloud forest and dwarf forest. Most collections of this species are from samples of sifted leaf litter taken from the forest floor, but a few specimens are known from cookie bait cards. Nests have never been found, but dealate queens are common in the leaf litter, suggesting that nests might occur within this stratum.
Comments. Stenamma picopicucha looks like a cross between S. crypticum and S. ignotum. The petiole and anterior clypeal margin are more like S. crypticum, but the basal margin of the mandible and gastral pilosity are more similar to S. ignotum. I originally intended to lump this species in with S. crypticum until I noticed that the two species occur in sympatry near the peak at Cusuco in Honduras. It is interesting to note that this mountaintop population at Cusuco has the postpetiole bulging and smooth; as a consequence, I label this form variant 1 (Figure 143). This population is most likely the same as S. picopicucha based on mandible and clypeus structure. More normal-looking specimens occur at lower elevation on the mountain.    lobes of moderate width , not obscuring torular lobes in full-face view; head appearing subrectangular (CI 84-89), with posterior margin depressed medially; eyes small (EL 0.05-0.09, REL 10-16), subcircular to slightly ob-long, with 3-5 ommatidia at greatest diameter; face densely sculptured, usually mostly rugoreticulate, with longitudinal rugae medially, but sometimes reticulae less distinct and interconnected, interstices lightly punctate; scape relatively short, not reashing posterior margin of head when laid back (SI 81-92), usually of average thickness (type population), but some populations with scape distinctly swollen distally; scape cuticle mostly smooth and somewhat shiny, with scattered piligerous punctae; flagellum with somewhat distinct 4-segmented antennal club, apical segment noticeably enlarged; sculpture on mesosoma variable among populations, lateral surface usually weakly to strongly punctate, with variable number of longitudinal rugulae, dorsal surface of promesonotum variably rugulose-punctate, with pronotum ranging from completely smooth to strongly sculptured, most populations intermediate (type population), pronotum sometimes with a distinct longitudinal carina; propodeal declivity smooth and shiny or with a few transverse carinulae; promesonotum in profile low-domed and roughly symmetrical (type population), or less often flattened and more asymmetrical, with anterior face distinctly longer than posterior; propodeal spines tuberculate or forming short, broad triangular spines (PSL 0.07-0.14, PSI 1.5-2.3); metanotal grove usually well demarcated, of moderate depth and width; petiole of moderate length (PL/HW 0.47-0.56), average-looking; node in profile somewhat small (PH/PL 0.57-0.64), subconical, with anterior face slightly longer and more sloping than posterior face, node dorsum in profile rounded, pointing vertical to slightly posteriad; postpetiole in profile subcircular, usually appearing similar in size to petiolar node (type population), but sometimes slightly larger and more bulging (PPH/PH 0.86-1.08); petiole and postpetiole lightly to somewhat strongly punctate, with nodes variably smooth and shiny; gaster mostly smooth and shiny, with scattered piligerous punctae; most of body dorsum with very short suberect to decumbent pilosity; scapes with a dense layer of decumbent to appressed setae; gastral pilosity consisting of a dense decumbent (type population) to appressed layer of setae, and a much sparser layer of suberect setae, which is sometimes difficult to see among decumbent setae; setae on legs mostly appressed, with a few suberect setae on coxae and femoral venters. Same as worker except for standard queen modifications and as follows: pronotum transversely rugose to rugoreticulate laterad, becoming punctate mesad; mesoscutum with narrow strip of smooth cuticle extending from anterior margin to about midpoint along midline; mesopleuron mostly smooth and shiny; propodeum mostly with transverse carinulae that wrap around surface, or less often mostly punctate; propodeal spines smaller (PSL 0.10-0.11, PSI 1.3-1.8).

Male. Unknown.
Biology. Stenamma saenzae is known almost exclusively from extracts of sifted leaf litter, with only a few queens collected from flight intercept traps in Belize. It is restricted to montane wet forest environments (e.g. cloud forest, mesophyll forest, pine cloud forest, oak-pine forest, liquidambar-oak-pine forest) and has been collected from 1000-2100 m elevation. Dealate queens as well as workers are commonly collected from leaf litter, suggesting that nests might be located within this stratum.
Comments. Based on overall size and form, S. saenzae might be confused with S. crypticum, S. nanozoi, or S. excisum, but out of these species, S. nanozoi is the only species to share the small tooth on the basal margin of the mandible. Stenamma saenzae can be easily separated from S. nanozoi by comparing gastral pilosity, which in the latter species, is composed mainly of a sparse layer of thickened suberect setae. Tentative molecular phylogenetic results show S. saenzae as sister to a clade that includes S. catracho, S. crypticum, and S. monstrosum (Branstetter unpublished data).
Stenamma saenzae shows considerable morphological variability among populations. From this variation, I describe two variants that differ significantly from the type phenotype (indicated above). Variant 1 ( Figure 147A-C) occurs mainly in central Guatemala (Biotopo Quetzal, Purulhá) and has the following distinguishing features: pronotal dorsum smooth and shiny; postpetiole more bulging, appearing larger than petiolar node; head somewhat enlarged. Although distinct from the type population, I find intermediate phenotypes at intervening localities, causing me to conclude that this variation is probably intraspecific, and likely due to environmental effects on size and sculpture. Supporting this view is the observation that the locality Biotopo Quetzal, where variant 1 is most distinct, is an especially cool, wet cloud forest site.
Small-sized species; general body color dark brown to brown, with appendages lighter, brown to yellow-brown toward extremities; setae golden brown; mandible usually with 6 distinct teeth, basal tooth well-defined; basal margin of mandible sinuous, with a distinct basal notch and accompanying small inner tooth; mandible mostly smooth, except for scattered piligerous punctae, and several striae around the base and lateral surface; anterior clypeal margin in anterodorsal view forming 4 small teeth (only outer teeth visible in full-face view); median clypeal lobe with faint longitudinal carinulae that diverge toward anterior margin, apex of lobe with a short and long transverse carinula, area in between transverse carinula and anterior clypeal margin forming a distinct cavity for mandibles, remainder of clypeal surface mostly smooth; posterior extension of clypeus between antennal insertions of moderate width (PCW 0.03-0.04), with sides subparallel; frontal lobes of moderate width (FLD 0. , not covering torular lobes in full-face view; head subcircular to oval-shaped (CI 90-96), with posterior margin distinctly depressed; eye of moderate size (EL 0.10-0.14, , with 4-5 ommatidia at greatest diameter; face mostly covered with many short to long longitudinal carinulae and rugulae, posterior margin and posterolateral surfaces smooth and shiny; scape of moderate length (SI 87-94), not quite reaching posterior margin when laid back; scape surface mostly shiny, with some faint striations, and scattered piligerous punctae; flagellum with a distinct 4-segmented antennal club; promesonotal dorsum with longitudinal and arcuate carinulae, that usually wrap around a central patch of smooth cuticle, but sometimes entire dorsum sparsely carinulate, side of pronotum mostly smooth, mesopleuron and side of propodeum with variably developed punctae and rugulae, sometimes mesopleuron mostly smooth, propodeal dorsum and declivity with some transverse carinulae; promesonotum in profile low-domed, and roughly symmetrical; metanotal groove in profile of moderate width and depth, often with a small central welt (metanotum); propodeal spines reduced to small tubercles (PSL 0.07-0.09, PSI 1.1-1.3); dorsal edge of propodeal lobe in profile markedly elongate; petiole in profile appearing of moderate to long length (PL/HW 0.45-0.51); petiolar node of moderate height (PH/PL 0.58-0.65), slightly asymmetrical, with anterior face longer and more sloping than posterior face, dorsum of node gently rounded, always pointing distinctly posteriad; postpetiole in profile appearing similar in size to petiolar node (PPH/PH 0.83-0.94), subspherical, with anterior face only slightly longer than posterior face; petiole and postpetiole mostly lightly punctate, with some rugulae around nodes, anterior faces of nodes and dorsum of peduncle mostly smooth; gaster mostly smooth and shiny, with scattered piligerous punctae; face pilosity short, with a layer of suberect setae, and a denser layer of decumbent setae; setae on mesosoma and gaster mostly long and suberect, gaster with a sparse layer of decumbent setae; scape setae uniformly subdecumbent; setae on legs mostly subdecumbent, with a few suberect setae on femoral venters and coxae. Same as worker except for standard queen modifications and as follows: pronotum with transverse carinulae/rugulae; mesoscutum mostly with longitudinal carinulae/rugulae, sometimes humeral area mostly smooth, with only piligerous punctae; scutellum smooth in center, longitudinal rugulae elsewhere; propodeum with transverse carinulae that wrap around surface; mesopleuron mostly smooth; pilosity on gastral tergites clearly bilayered with a dense layer of short, subdecumbent pubescence, and a relatively sparse layer of longer suberect setae (not as long as in worker); wing venation as in Figure 151D.
Male. See Figure 151E-G. Biology. Stenamma sandinista is a specialist of montane wet forest habitats (e.g. cloud forest, dwarf forest, mesic forest) and is known from approximately 900-1600 m elevation. Nearly all collections are from sifted leaf litter taken from the forest floor. Only once in dwarf cloud forest habitat have I found a nest fragment. It was in leaf litter and was located by randomly scraping back the top layer of leaves while collecting a Winkler sample. The nest had tens of workers and brood.
Comments. Stenamma sandinista can be separated from similar forms by its eye size, mandibular structure, facial sculpture, and gastral pilosity. Geography is also useful, as it is present at only a few high-elevation sites within Nicaragua.
Given the complexity of the S. schmidti complex (see below), it is possible that S. sandinista is a high-elevation, allopatric variant of S. schmidti. However, I describe it as a new species for the following reasons: it occurs at several sites within Nicaragua and maintains a consistent phenotype; it is sympatric at Cerro Musún with a somewhat distantly related S. schmidti variant that occurs from Costa Rica to Nicaragua; and its sister species, S. nanozoi, is quite divergent and restricted to the lowlands of Honduras.  Stenamma schmidti Menozzi, 1931a: 198, fig  Worker diagnosis. Note that this species is highly variable. See comments section below discussing morphological variants. Integument mostly dark brown, red-brown, or brown; small-to medium-sized species; petiolar node in profile usually broadly rounded and distinctly angled posteriad; postpetiole in profile subspherical; propodeal spines absent to tuberculate (PSL 0.06-0.13, PSI 0.8-1.5); basal margin of mandible usually with a distinct basal notch and small accompanying tooth, but sometimes with only a small notch, or with basal margin sinuous. If basal margin of mandible with notch and tooth then: anterior clypeal margin forming 2-4 sharp to blunt teeth, with outer teeth more projecting; eye of moderate to large size (EL 0.10-0. 18,, with 6-10 ommatidia at greatest diameter. If basal margin with small notch, but no tooth then: face completely sculptured, densely rugoreticulate; mesosoma mostly sculptured, punctate-rugulose; pilosity on first gastral tergite sparse, mostly stout and suberect, with only a few decumbent setae. If basal margin of mandible sinuous (without notch and tooth) then: anterior clypeal margin with a simple median emargination; propodeal spines absent, reduced to blunt angles where propodeal dorsum and declivity meet; eye large (EL 0. , with 8-11 ommatidia at greatest diameter; face usually completely sculptured, but sculpture never very dense, mostly carinulatepunctate; carinulae usually longitudinal, but some specimens with transverse carinulae on anterior half of head; pronotum either completely carinulate-punctate, lightly punctate, or completely smooth; carinulae when present usually transverse in orientation; some specimens noticeably long and gracile, with scape, metafemur, and petiole relatively long (SI 107-121, 86-93; PL/HW 0.58-0.63); gastral pilosity mostly sparse and suberect, with only a few decumbent to appressed setae; erect setae often stout. Geographic range. Nicaragua to Ecuador.  (86), SI 85-121 (97), , , PSI 0.8-1.5 (1.1), MFI 71-108 (96), ACI1 62-68 (66), .
Small-to medium-sized species; general body color dark brown, to red-brown, to brown, with appendages brown to orange-brown, lighter at joints and toward extremities; setae golden; mandible with 5-7 teeth (usually 6), with basal tooth often appearing bidentate, inner teeth sometimes worn and indistinct; basal margin of mandible usually sinuous, with a distinct basal notch and accompanying small tooth (type population), but sometimes with a basal notch and no tooth, or only sinuous; mandible mostly smooth and shiny, with scattered piligerous punctae and a variable number of basal and lateral striae; anterior clypeal margin usually forming 2-4 sharp to blunt teeth (type population), but sometimes nearly flat, or with a simple median emargination; median clypeal lobe usually rather distinct, and produced slightly over anterior clypeal margin in full-face view (type population), but sometimes obliquely flattened and not produced; dorsal surface of lobe mostly smooth and shiny (type population), or with a variable number or irregular carinulae, apex of lobe with a short to long transverse carina; area in between carina and anterior clypeal margin, usually forming a distinct cavity where mandibles insert (type population); remainder of clypeal surface mostly smooth; posterior extension of clypeus between antennal insertions of narrow to moderate width (PCW 0.02-0.06; type population), with sides subparallel; frontal lobes moderate (type population) to slightly expanded (FLD 0.11-0.25; FLI 21-33), not greatly covering torular lobes in full-face view; head usually roughly oval-shaped (type population) to subcircular, with a distinct median depression in posterior margin, but head sometimes more elongate, with posterior margin flat (CI 79-94); eye of moderate to large size, sometimes relatively very large (EL 0.09-0. 18,, oval-shaped, often bulging, with 5-11 ommatidia at greatest diameter; face sculpture highly variable, ranging from mostly smooth and shiny, to densely rugoreticulate (type population with fine longitudinal carinulae on middle of head and on gena, posterior 1/5 of head smooth); scape ranging from relatively short and somewhat thick to long and slender (SI 85-121), not surpassing to distinctly passing posterior margin when laid back (moderate length in type population, just reaching posterior margin); scape surface with numerous piligerous punctae, but mostly shiny; flagellum with a distinct (type population) to very distinct 4-segmented antennal club; mesosomal sculpture highly variable, ranging from mostly smooth, to densely rugose-rugoreticulate (type population with promesonotum mostly smooth and shiny, at most a few longitudinal carinulae dorsally); mesopleuron and side of propodeum mostly smooth, with some faint punctae and carinulae, propodeal dorsum and declivity with light transverse carinulae; promesonotum in profile usually low-domed and roughly symmetrical; metanotal groove variable, usually welldemarcated and of moderate width and depth (type population), but sometimes deeper and better defined, with metanotum forming a small welt, or sometimes shallow and indistinct, with propodeum connecting almost continuously to promesonotum; propodeal spines absent to tuberculate (PSL 0.06-0.13, PSI 0.8-1.5; forming a sharp angle in type population); petiole in profile appearing of moderate length (type population) to somewhat elongate (PL/ML 0.48-0.63); petiolar node usually broadly rounded and pointing distinctly posteriad (type population), but sometimes appearing subquadrate and asymmetrical, with an apex occurring at anterior margin of dorsum; petiolar node similar in size to petiolar node and subspherical; petiole and postpetiole usually mostly smooth and shiny, with only a few faint punctae (type population), but sometimes mostly punctate, rugulae sometimes present on posterior half of postpetiolar node; gaster mostly smooth, with scattered piligerous punctae; most of body dorsum with standing pilosity; gastral pilosity highly variable, sometimes distinctly bilayered, with a sparse layer of stout suberect setae, and a dense layer of short, decumbent pubescence (type population), sometimes pubescence absent, leaving only stout, suberect setae and a few decumbent setae, or sometimes all setae of moderate thickness and with variable density and layering (suberect layer usually always present); setae on scape usually relatively dense, and uniformly subdecumbent to appressed; setae on legs decumbent to appressed, with some longer suberect setae on femoral venters and coxae. Same as worker except for standard queen modifications and as follows (only type population queen considered): pronotum with some transverse rugulae laterad; mesoscutum lightly punctate to foveolate, with a central line of smooth cuticle; scutellum with longitudinal carinulae laterad, and a central smooth patch; propodeum with transverse carinulae that wrap around entire surface; mesopleuron mostly smooth; pilosity on mesoscutum bilayered similar to gaster, with a layer of longer erect to suberect setae, and a layer of short, dense pubescence; wing venation as in Figure 155D.
Male. See Figure 155E-G. Biology. Stenamma schmidti, as defined here, is a rather variable species. It inhabits tropical wet forest environments from sea level to about 2400 m, becoming most abundant in cloud forest habitats above 800 m. At some cloud forest sites, S. schmidti can be one of the most common ant species occupying the leaf litter. Despite this fact, the species is very cryptic and finding nests is an uncommon event. Most collections of S. schmidti are from Winkler or Berlese samples of sifted leaf litter or epiphyte mats. Nest collections have been made, but these are very rare for the leaf-litter dwelling variants and only slightly more common for the arboreal forms. Nests are very small, with only tens of workers, and a single egg-laying queen. Workers, when encountered, are very slow moving and freeze upon disturbance. Additional natural history notes specific to particular morphological variants are described below.
Comments. The Stenamma schmidti complex is as remarkable as it is maddening, comprising an amazing radiation of forms, which together occupy more morphospace than all of the Holarctic clade Stenamma species combined. Because many putative morphospecies appear to occur in sympatry, it is tempting to separate S. schmidti into multiple species. But after careful review of many specimens and populations, accompanied by molecular phylogenetic data, I find it very difficult to divide up the complex in a satisfactory way. A major reason for this is the existence of specimens with intermediate phenotypes, forming what appears to be a morphological continuum. Consequently, I have decided to delimit a single polytypic species composed of many variants (described below). Several of these variants may constitute good species, but I believe more genetic and distribution data are needed (especially from Panama and South America) to adequately assess the distinctness of all forms in the complex.
The difficulty in resolving species boundaries in the complex probably stems from several factors, including phenotypic plasticity, morphological convergence, hybridization, and sampling bias. It could also be that if the group represents a recent radiation, there has been insufficient time for some species to reach monophyly. Based on my observations so far, I favor the idea that there are several weakly differentiated forms that occasionally come into contact and hybridize.
An interesting observation about diversification within the schmidti complex is that it seems particularly prone to convergence, with specimens from a particular elevation and microhabitat having similar morphological characteristics. For example, S. nanozoi and variants 7 and 8 of S. schmidti are all small, have densely sculptured faces, and have the gastral pilosity forming a single sparse layer of stout, suberect setae. All of these taxa occur at low elevation from sea level to approximately 1000 m. Counter to expectations, phylogenetic data show that they are not closely related to one another, with S. nanozoi sister to S. sandinista, and variants 6 and 7 of S. schmidti both more closely related to other high-elevation variants (Branstetter unpublished data). This suggests that the characteristics one would probably use to unite these taxa as a single species are convergent, and thus misleading.
By combining many divergent forms into a single species, it has made characterizing S. schmidti rather difficult due to its large phenotypic range. Most specimens that closely match one of the variants below should be identifiable as S. schmidti, but specimens with intermediate phenotypes will probably not key out easily.
It will also be hard to adequately separate S. schmidti from the closely related S. nanozoi and S. sandinista, as well as from the similar looking S. saenzae, based only on morphology. The characters in the key and diagnosis will work for most specimens, but not all. Fortunately, geography should clarify matters, as most of the schmidti complex occurs farther south than the other species. Only S. sandinista is found in sympatry with variant 6 of S. schmidti. These two species both occur at Cerro Musún in Nicaragua, where they are separated by elevation, with S. schmidti occurring below about 800 m and S. sandinista occurring above 900 m.
Defining features of the holotype's morphology ( Figure 152C, D, F) are indicated in the species description above (see parenthetical comments), but main characteristics are as follows: basal margin of mandible with distinct notch and small accompanying tooth; anterior clypeal margin forming 2-4 teeth; median lobe of clypeus produced slightly over anterior clypeal margin in full-face view; head roughly oval-shaped to subcircular (CI 85-93); scape of moderate length (SI 85-97); eye large (EL 0. , with 6-9 ommatidia at greatest diameter; face sculpture mostly lightly carinulate, with posterior half or less of head usually smooth; mesosoma mostly smooth, with some faint carinulae/rugulae variably present; gastral pilosity distinctly bilayered, with a sparse layer of suberect setae, and a dense layer of decumbent pubescence. The holotype appears to be a small, less robust specimen of S. schmidti, with much of the face and mesosoma smooth. A paratype specimen I observed from the same series as the holotype is slightly larger and has more developed sculpture, with the face carinulae extending close to the posterior margin of the head. What I consider to be the holotype form of S. schmidti is a high-elevation morphospecies occurring in leaf litter from 1500 to over 2000 m. I have observed similar specimens from multiple sites in Costa Rica and in Panama. Specimens from the Cordillera de Talamanca in south- ern Costa Rica (e.g. Las Alturas, Altamira, Pittier) and from northern Panama (e.g. Cerro Punta, Hartman Finca) usually have more sculpture on the face and mesosoma. Molecular phylogenetic data show some clustering of specimens from Central Costa Rica, but specimens from southern Costa Rica and Panama are scattered throughout the tree. Nests of this form are almost unknown. Longino (pers. comm.) has reported finding a nest in the root disc of a fallen tree.
Variant 1 ( Figure 153A-C) is a densely sculptured version of the holotype form. It varies as follows: face completely sculptured, with dense costulae in middle changing to rugoreticulae toward sides; pronotum with dense longitudinal costulae/rugulae, sometimes with a patch of smooth cuticle on side and middle of dorsum; mesonotum rugoreticulate; katepisternum mostly smooth; side of propodeum rugose; dorsum and declivity of propodeum transversely carinulate; petiole and postpetiole mostly punctate. Variant 1 occurs at multiple sites in Costa Rica and northern Panama and seems to occur only at mid-elevations from 800-1500 m. It is known only from samples of sifted leaf litter.
Variant 2 ( Figure 153D-F) is a more robust version of variant 1. It differs as follows: body color darker; sculpture deeper, more developed; petiolar node thicker, more robust; propodeal lobes and spines in profile view noticeably broader; frontal lobes somewhat expanded, almost completely covering torular lobes in full-face view; layer of pubescent setae on gaster absent, with only a few short decumbent setae present under stout, suberect setae. This variant is known from sites in southern Costa Rica and northern Panama and occurs at mid-elevations between 1000-1500 m. It is known only from samples of sifted leaf litter.
Variant 3 ( Figure 153G-I) is similar to variant 2, except as follows: sculpture on pronotal dorsum distinctly transverse and arcuate; sculpture on side of propodeum more dense and oriented so that it wraps up and over the dorsal surface; promesonotum in profile view slightly more robust, and more distinctly separated from metanotal groove. Variant 3 occurs at multiple sites in Costa Rica at mid-elevations between 1000-1500 m. Results from molecular phylogenetic data show that specimens of variant 2 and 3 from several sites in Costa Rica form a clade nested inside the schmidti complex. This might be evidence that these two variants represent a single good species. However, it is strange that the very similar looking variant 1 does not cluster with variant 2 and 3. A broader sampling of specimens from Costa Rica and especially Panama is needed to further investigate species boundaries. This variant is known only from samples of sifted leaf litter.
Variant 4 ( Figure 153J-L) is similar to the holotype form, except as follows: face and mesosomal sculpture usually reduced, with posterior half of face mostly smooth; notch in basal margin of mandible very deep; anterior clypeal margin forming 4 distinct teeth, with outer teeth strongly projecting (presumably to fit in notch in basal margin of mandible); gastral pilosity mainly forming a single sparse layer of stout, suberect setae. This variant seems to be an arboreal version of the holotype form of S. schmidti, with most specimens coming from canopy fogging samples or Winkler samples of epiphytic material. Some specimens are also known from litter samples taken from the forest floor. Variant 4 occurs mainly at mid elevations at Monteverde and Volcán Barva in Costa Rica. Specimens from the canopy at Monteverde are rather uniform in morphology, but specimens from the forest floor at Monteverde and on Volcán Barva are more variable and become difficult to assign to a particular variant with certainty. These difficult specimens have intermediate sculpture and gastral pilosity.
Variant 5 ( Figure 153M-O) differs drastically from the holotype form and is potentially a good species nested within the schmidti complex. It has the following characters: basal margin of mandible sinuous, without a basal notch or tooth; anterior clypeal margin with a simple median emargination; head more elongate and narrow (CI 79-84), with posterior margin flat; eye large (EL 0. ; scape long, surpassing posterior margin of head when laid back (SI 107-121); propodeal spines absent, at most forming blunt angles; mesosoma noticeably elongate and gracile; petiole noticeably elongate; sculpture on head and mesosoma carinulate-punctate; face sometimes with transverse carinulae on anterior half; pronotum with transverse carinulae; legs elongate (MFI 71-80); gastral pilosity forming a single sparse layer of stout, suberect setae. This variant is known only from Monteverde and Volcán Barva in Costa Rica from 1000-1500 m. It is apparently an arboreal form of S. schmidti with specimens collected from fogging samples and from nests found under epiphytes in the canopy. Longino (pers. comm.) has reported that this variant prefers to nest under small epiphyte clumps on small branches. Molecular phylogenetic results show specimens from Monteverde and Volcán Barva clustering together, suggesting some reproductive isolation. However, I find specimens with intermediate morphology between this variant, the holotype form, and variant 4. Some specimens have the anterior clypeal margin forming sharp teeth, or the mesosoma stockier and less gracile. Counter to expectations, the intermediates do not cluster with variant 5 specimens in the phylogeny.
Variant 6 ( Figure 154A-C) is similar to variant 5 in that it has the same mandible and clypeus structure, it lacks propodeal spines, and it has a relatively large eye. However, it has the following differences: smaller overall size; mesosoma less elongate and gracile; head roughly oval-shaped, less elongate (CI 85-87); scape and metafemur relatively smaller (SI 94-101, MFI 86-93); gastral pilosity not stout; sculpture reduced, usually faintly punctate or smooth. Variant 6 like variant 5 is known only from Monteverde and Volcán Barva in Costa Rica, and it is arboreal, with specimens collected from fogging samples and nests in epiphyte clumps. Molecular phylogenetic data show specimens from Monteverde and Volcán Barva clustering together. But, despite the similarities with variant 5, the two variants do not cluster together. I would not be surprised if variant 6 is a hybrid between variant 5 and the holotype form of S. schmidti or variant 7. It may also be a distinct species that has convergently evolved some features of variant 5. Variant 7 ( Figure 154D-F) is a smaller, low-elevation version of the holotype form. It has the following differences: smaller overall size; face completely sculptured, with carinulae in middle changing to rugoreticulae toward lateral margin; dorsum of promesonotum usually with carinulae encircling margins (humeri), remainder of promesonotum smooth; eye sometimes relatively very large (EL 0. ; gastral pilosity mainly a single sparse layer of stout, suberect setae, with a few decumbent setae underneath. This variant occurs from sea level to about 1000 m elevation and has been collected at multiple sites in Nicaragua and Costa Rica. It is very similar to variant 8, S. nanozoi, and specimens from lowland Panama, Colombia, and Ecuador, but molecular phylogenetic data do not cluster all of these similar-looking forms together. Only specimens from lowland Nicaragua and northern Costa Rica form a clade. This variant is distinct and easy to identify at low elevations, but at mid elevations in Costa Rica, especially on Volcán Barva, it becomes very difficult to separate this variant from the holotype form or several of the other variants. Some of this difficulty might be because smaller specimens of the other variants look like variant 7, but I suspect it is also because of hybridization and perhaps adaptation of variant 7 to the higher elevation environment. Nearly all specimens of this variant are known from leaf litter, but one nest was found at the La Selva Biological Station in Costa Rica. It was in a small branch in the leaf litter (Longino, pers. comm.).
Variant 8 ( Figure 154G-I) is a small version of S. schmidti and is superficially similar to variant 7, but differs as follows: face mostly rugoreticulae; mesosoma more sculptured, mostly punctate to rugulose-punctate; eye usually smaller , with 5-6 ommatidia at greatest diameter; basal margin of mandible sometimes with only a small basal notch and no tooth; anterior clypeal margin sometimes appearing flat, without defined teeth. This variant mainly includes specimens from the Osa Peninsula in Costa Rica (13 km SSW Pt. Jimenez), but many lowland specimens from Panama to Ecuador are similar, with some variation in sculpture and mandible and clypeus structure. Despite similarities with variant 7, molecular phylogenetic data do not show these two variants clustering together, suggesting that their similar morphology is convergent. I find some similarities in mesosoma shape and sculpture between variant 8 and high-elevation specimens from southern Costa Rica that I assign to the holotype form of S. schmidti. Perhaps overall size and pilosity are misleading characters in the schmidti complex.
Variant 9 ( Figure 154J-L) is a mid-to high-elevation version of variant 8. It differs as follows: larger overall size (similar to holotype form); eye larger (EL 0. ; dorsum of promesonotum with transverse arcuate carinulae; pilosity on gastral dorsum distinctly bilayered, with a sparse layer of somewhat stout suberect setae, and a layer of dense decumbent to appressed pubescence (compared to type  of moderate to shallow width and depth; propodeal spines reduced to sharp angles or short tubercles (PSL 0.09-0.11, PSI 0.9-1.2); petiole and postpetiole robust, with nodes somewhat bulging; petiole of moderate length (PL/HW 0.45-0.58); petiolar node in profile usually subconical (type population), roughly symmetrical, with dorsum forming a well-defined apex that points vertically, but sometimes dorsum with a broadly rounded top that points slightly posteriad; postpetiole in profile subspherical, usually similar in same size to petiolar node (PPH/PH 0.79-0.93); petiole and postpetiole punctate, with anterior faces of nodes smooth and shiny; gaster mostly smooth and shiny, with scattered piligerous punctate; most of body dorsum with a layer of medium to short standing pilosity; scape with a uniform layer of subdecumbent to decumbent setae; gaster with a sparse layer of stout suberect setae, and sometimes a few underlying short decumbent setae; leg setae mostly appressed, with suberect setae on coxae and femoral venters.
Queen. Unknown. Male. Unknown. Biology. A rare species, S. stictosomum is a cloud forest specialist known from a few samples of sifted leaf litter, a beating sample, and from quarantine in Brownsville, TX. The latter specimen was found on orchids being shipped to the United States from either Oaxaca or San Luis Potosí, México. Collections range from 1450-1750 m elevation. The presence of S. stictosomum on orchids and on vegetation (beating sample) suggests that it may nest or at least forage arboreally. This would help explain why the species appears to be so rare, despite being rather widespread.
Comments. Stenamma stictosomum may form a complex of species, as evidenced by the significant amount of morphological variation among populations. However, an adequate assessment of species boundaries is impossible because so little material has been collected of the species (10 specimens from 7 localities). Consequently, I describe a single species here, but discuss some of the among population variation below.
The type population (20.6km SW Valle Nacional) is the most distinctive, with the head and mesosoma entirely coarsely punctate and without well-defined carinulae (except for the propodeal dorsum and declivity). In the right lighting, these specimens give off a bluish reflectance from the surface sculpturing.
Variant 1 ( Figure 158A-C) is a specimen from quarantine, likely originating from Oaxaca or San Luis Potosí, Mexico. It is similar to the type population, but has reduced sculpture overall (less coarse, more polished) and carinulate punctate sculpture on the promesonotum.
Variant 2 ( Figure 158D-F) is from Guatemala (a single specimen). It is similar to the type population, except that the punctae are less coarse (more polished, somewhat effaced) and there are smooth patches of cuticle on the side of the head and pronotum. Also, the petiolar node in profile has a rounded dorsum that points slightly posteriad.
Variant 3 ( Figure 158G-I) is from Veracruz, Mexico (a single specimen) and is coarsely sculptured, but the sculpture is carinulate punctate, with the carinulae emerging out of the borders of the punctae. The carinulae on the promesonotal dorsum are indistinctly transverse in orientation and the carinulae on the pronotal side are arcuate.
Variant 4 ( Figure 158J-L) is from Hidalgo and San Luís Potosí, Mexico. All specimens are similar in that the sculpture is mainly carinulate or rugulose (mostly lon-   Worker diagnosis. Integument brown (probably darker in recently collected specimens); small to medium-sized species (see HL, ML, PrW below); head, mesosoma, and gaster mostly smooth and shining, with petiole and postpetiole punctate; promesonotum in profile distinctly asymmetrical, with anterior face gently rounded, dorsal surface flat or only slightly curving, and posterior face short, straight and forming a relatively sharp angle with dorsal surface; median lobe of clypeus bicarinate, projecting, and with a broad and rather deep median emargination at anterior margin; basal margin of mandible straight, without notch or substantial depression; petiolar node distinctly angled posteriad; postpetiole in dorsal view, with distinct mesolateral angles and a longitudinal lobe, giving anterior half of postpetiole a distinct pinched- in appearance; eye of moderate size (EL 0.10-0. 12,, oval shaped, with 5-6 ommatidia at greatest diameter; setae on gastral tergites of moderate length and density, suberect to subdecumbent; propodeal spines absent, forming at most an ob-tuse angle in profile view (PSL 0.06-0.07, PSI 1.0-1.3); frontal lobes narrow (FLD 0. , not obscuring torular lobes in full-face view (FLD 0.14-0. 15, (89), , , FLI 24-25 (25) Small-to medium-sized species; general body color brown to light brown, with extremities becoming yellow-brown (note that all studied specimens are over 40 years old, the color of fresh specimens must be darker); setae golden; mandible with 6 teeth, consisting of 3 distinct apical teeth, a somewhat projecting basal tooth, and 2 inner teeth, which are often worn and indistinct; basal margin of mandible relatively straight, without notch or significant depression; dorsal surface of mandible mostly smooth and shining, with scattered piligerous punctae and a few short basal striae; median lobe of clypeus bicarinate, projecting, and with a broad and rather deep median emargination at anterior margin, apex of lobe with a transverse carina, area between carinae distinctly depressed; carinae on median lobe forming a distinctive triangular shape in anterodorsal view; remaining surface of clypeus mostly smooth and shiny; posterior extension of clypeus between frontal lobes somewhat narrow (PCW 0.03-0.05), with subparallel sides; frontal lobes narrow, not obscuring torular lobes in full-face view; head roughly oval-shaped (CI 88-91), posterior margin flat to slightly concave, never greatly depressed medially; eye of moderate size (EL 0.10-0. 12,, oval-shaped, with 5-6 ommatidia at greatest diameter; face nearly completely smooth and shiny, with scattered piligerous punctae and a few longitudinal carinulae around frontal carinae and on genae; scape distinctly shorter than HW (SI 86-92), not quite reaching posterior margin of head when laid back; scape surface mostly smooth and shiny, except for scattered piligerous punctures and faint striae; flagellum with distinct 4-segmented antennal club; mesosoma mostly smooth and shining, except metanotal groove with several longitudinal carinae, metapleuron with faint punctae, and propodeal dorsum and declivity with faint transverse carinulae; promesonotum in profile distinctly asymmetrical, with anterior face gently rounded, dorsal surface flat or only slightly curving, and posterior face short, straight and forming a relatively sharp angle with dorsal surface; metanotal groove distinct, but not very deep; propodeal spines essentially absent (PSL 0.06-0.07, PSI 1.0-1.3), forming at most obtuse angles at transition between dorsal and declivitous faces of propodeum in profile; petiole of moderate length (PL/ HW 0.51-0.57), node of moderate size (PH/PL 0.62-0.67) and distinctly angled posteriad, with anterior face slightly longer and more sloping than posterior face, node dorsum broadly rounded; postpetiole in profile asymmetrical, with long sloping ante-rior face and short nearly vertical posterior face; postpetiole in dorsal view with distinctive mesolateral angles and a longitudinal lobe, giving the anterior half of postpetiole a distinct pinched-in appearance; anterior faces of petiole and postpetiole smooth and shiny, remaining surfaces faintly punctate; most of body with a thin layer of short to medium length standing setae; pilosity on gastral tergites somewhat bilayered, with a layer of longer suberect setae, and a layer of equally dense subdecumbent setae; facial setae short and mostly decumbent; setae on scape subdecumbent to decumbent; setae on legs suberect to appressed, with longer suberect setae on femoral venters and coxae.  Biology. Stenamma tiburon is known only from a single Berlese sample collected from forest at 1650 m elevation.
Comments. The combination of sculpture, clypeus structure, and postpetiole structure make S. tiburon a very distinctive species that should not be confused with any other MAC species. I include S. pelophilum as a similar species only because both species occur in the same couplet of the key, but these species are very different and can be easily separated by comparing clypeus structure.
It should be noted that this species is known from only nine specimens that were collected in 1969. Thus, the coloration described here is certainly different from what fresh specimens probably look like. Further more, this species has not been included in molecular analyses and it is somewhat uncertain to which species it is most closely related. However, because the postpetiole has a distinct dorsal lobe I include S. tiburon in the lobinodus species group (diagnosis of group given under S. lobinodus above) and I hypothesize based on distribution and morphology that is sister to S. lobinodus.
Material examined. Known only from the type locality.  (88). Medium-sized species; general body color black to red-black, with brown patches on waist and gaster; mandibles, clypeus and appendages dark brown to yellow-brown; setae golden; mandible with 6-7 teeth, consisting of 3 distinct apical teeth, a basal tooth, and 2-3 inner teeth, which are often worn and indistinct; basal margin of mandible straight, without any notch or significant depression; dorsal surface of mandible mostly smooth and shiny, with scattered piligerous punctae and variable number of basal striae; median lobe of clypeus with a pair of vestigial longitudinal carinulae and/ or several ill-defined rugulae, apex of lobe with a short transverse carinula, remainder of clypeus smooth and shiny; posterior extension of clypeus between frontal lobes rather broad (PCW 0.06-0.07), with subparallel sides; frontal lobes relatively well developed, but not markedly expanded dorsolaterally (as in S. diversum), nor completely obscuring the underlying torular lobes in full-face view; head roughly oval-shaped, slightly, but distinctly longer than broad (CI 87-93), posterior margin gently convex, never depressed medially; eyes relatively large and somewhat bulging (EL 0. , oval-shaped, with 7-10 ommatidia at greatest diameter; face mostly smooth and shining, with variable amount of weak carinulae/rugulae and punctae confined to lower ¾ of head; most specimens with some carinulae around antennal sockets and on gena, others with more extensive carinulae fanning outward from frontal carinae, sometimes with reticulae between antennal carinae and eyes; scape relatively long (SI 95-103), reaching and slightly surpassing posterior margin of head when laid back; dorsal surface of scape striate; flagellum with distinct 4-segmented antennal club; mesosoma shiny, almost entirely reticulately costate to coarsely rugoreticulae; propodeal declivity smooth, sometimes with a few transverse carinulae; promesonotum in profile low-domed and roughly symmetrically, anterior slope a little steeper and longer than posterior slope; propodeal spines reduced to small upward projecting points, or only forming sharp right angles where dorsal and declivitous surfaces of propodeum meet (PSL 0.14-0.18, PSI 1.4-1.9); petiole moderately long (PL/HW 0.57-0.63) and robust, node roughly half length of petiole and asymmetrical, with anterior face long and gradually sloping, and posterior face nearly vertical, but slightly angled so that apex of petiole points posteriad; dorsum of petiolar node viewed from posterior side weakly rounded; postpetiole in profile similar in size to petiolar node (PPH/PH 0.91-0.97), roughly circular, although with anterior face slightly longer and more sloping than posterior face; petiole and postpetiole shiny, nodes mostly smooth, with some rugulae and faint punctae on sides; venter of petiole and postpetiole weakly punctate; gaster mostly smooth and shiny, with scattered piligerous punctae; most of body with single layer of long standing setae; setae on legs and scapes varying from predominately suberect to mostly decumbent; coxae and femoral venters always with a row of longer suberect setae.
Queen description.  Small-to medium-sized species; general body color black, or dark brown to redbrown (type population), with appendages brown to orange-brown or yellow-brown, lighter in joints and toward extremities; setae golden brown; mandible with 6 teeth, 2 teeth nearest basal tooth sometimes more worn and less distinct, basal tooth often well-defined, projecting; basal margin of mandible usually sinuous, with a slight basal depression (type population), but without a tooth, some populations with basal margin almost straight; mandible mostly smooth, with scattered piligerous punctae, and some striations near base and along lateral surface; median lobe of clypeus with a pair of faint longitudinal carinulae that diverge anteriorly, apex of lobe with a short transverse carinula, remainder of clypeus mostly smooth; area in between median lobe and anterior clypeal margin forming a distinct concavity where mandibles insert; posterior extension of clypeus between frontal lobes of moderate width (PCW 0.04-0.06), with sides subparallel; frontal lobes of moderate width , not greatly covering torular lobes in full-face view; head roughly oval-shaped (CI 89-96), with posterior margin flat to slightly depressed medially; eye of moderate size (EL 0.10-0. 15,, oval-shaped, with 5-8 ommatidia at greatest diameter; face usually strongly sculptured, mostly rugoreticulate, with some longitudinal rugae along midline (type population), some populations with sculpture somewhat polished and reticulate less distinct; scape of moderate length (SI 85-98), just reaching posterior margin of head when laid back; surface of scape mostly smooth, with scattered piligerous punctae; flagellum with distinct 4-segmented antennal club; mesosoma usually completely sculptured (type population), but some populations shinier overall and with pronotum mostly smooth and shiny; pronotal dorsum longitudinally rugose, with rugae dense to somewhat sparse and irregular, rugae usually becoming punctae and reticulae on dorsum of mesonotum; side of pronotum mostly punctate or rugose, often with a small to large patch of smooth cuticle on ventral half; mesopleuron and side of propodeum rugulose-punctate; propodeal dorsum with rugoreticulae near anterior margin, changing to transverse carinulae near posterior margin; promesonotum in profile low-domed, slightly asymmetrical, with apex posterior of midpoint, anterior declivity of pronotum sometimes forming a sharp transition with dorsum, sculpture on declivity punctate, contrasting with rugose dorsum; metanotal groove usually welldemarcated, of moderate depth and width; propodeal spines tuberculate to short (PSL 0.08-0.16, PSI 1.1-1.8), often somewhat robust (type population); petiole in profile often distinctive, appearing somewhat elongate (PL/HW 0.53-0.56), with node broadly rounded and pointed posteriad, venter under node often with a small concavity; peduncle sometimes noticeably slender, thickening toward node; postpetiole in profile subspherical, similar in size to petiolar node (PPH/PH 0.85-0.91); anterior face of petiolar and postpetiolar nodes smooth, remainder of waist mostly punctate; gaster mostly smooth and shiny, with scattered piligerous punctae; pilosity on head, short and bilayered, with some longer suberect setae, and many shorter decumbent setae, remainder of body dorsum with longer suberect setae; pilosity on gastral dorsum predominately suberect and relatively sparse; setae on scape mostly subdecumbent; Same as worker except for standard queen modifications and as follows: pronotum with transverse rugae and rugoreticulae on lateral surface, changing to carinulae and punctae mesad; mesoscutum densely longitudinally rugose; scutellum rugose to rugoreticulate, sometimes with a smooth patch mesad; side of propodeum rugulose, with faint punctae, dorsum with transverse carinulae; wing venation as in Figure 167D.
Male. Unknown. Biology. This species is known only from Winkler and Berlese samples of sifted leaf litter. It occurs from approximately 1000-2000 m elevation and inhabits a variety of montane mesic forest environments (e.g. cloud forest, wet oak forest, oak-pine forest, tropical subevergreen forest, Liquidambar forest).
Comments. Stenamma vexator is not a particularly distinctive species, but it should be separable from similar species by the diagnostic character states given above and in the key. It bears the most resemblance to S. huachucanum, which occurs in sympatry with S. vexator at several sites. Stenamma vexator is usually larger than S. huachucanum and has a longer, more distinctive petiole. Molecular phylogenetic data tentatively show that S. vexator is sister to the diversum species group, which includes S. diversum and S. tico (Branstetter 2012, unpublished data).
Several aberrant populations are worth separating out as variants of S. vexator. Variant 1 ( Figure 166A-C) occurs at several sites in Puebla, Mexico. It has the propodeal spines tuberculate, the basal margin of the mandible nearly straight, and the clypeal teeth reduced to blunt nubs. Variant 2 ( Figure 166D-F) is known from a few collections taken at high elevation between Oaxaca and Valle Nacional, in Oaxaca, Mexico. It is larger, darker, and has reduced sculpturing, with the pronotum mostly smooth and shiny. It also has the propodeal spines tuberculate, and the petiolar node pointing more vertically. I have not seen intermediate specimens between this variant and the holotype form of S. vexator, so it is possible that this high elevation variant represents a distinct species. Variant 3 ( Figure 166G-I) is known from the locality Coapilla in Chiapas, Mexico. These specimens are black, have reduced sculpture, and have the propodeal spines almost absent. The petiolar node is also sharper and pointing more vertically. Placement of variant 3 within S. vexator is uncertain and needs to be confirmed with molecular data.  Medium to large-sized species; general body color mostly dark red-brown, with patches of brown and orange-brown on gaster, appendages lighter; setae golden brown; mandible with 6-9 teeth, consisting of 3 distinct apical teeth, a distinct basal tooth, and 2-5 inner teeth/denticles, which are usually worn and indistinct; basal margin of mandible straight to slightly sinuous, without a basal notch or depression; mandible mostly smooth and shiny, with scattered piligerous punctae and faint striae; anterior clypeal margin viewed from an anterodorsal angle with a median excavation containing 2 sharp outer teeth and 2 smaller inner teeth, which are sharp to blunt, and recessed behind median lobe of clypeus (not visible with mandibles closed); median lobe of clypeus usually with a pair of faint carinulae that diverge toward the anterior margin, apex of lobe with a short transverse carinula, remainder of clypeus mostly smooth and shiny, sometimes with a few additional rugulae on median lobe; posterior extension of clypeus between antennal insertions of moderate width (PCW 0.04-0.08), sides subparallel to slightly diverging posteriad; frontal lobes well-developed, but not completely covering torular lobes in full-face view (FLD 0.26-0.31, FLI 31-34); head appearing subrectangular (CI 86-92), with posterior margin depressed medially; eye relatively small (EL 0.10-0.13, REL 12-16), somewhat bulging, subcircular to slightly oval-shaped, with 6-8 ommatidia at greatest diameter; face usually strongly foveate to coarsely rugoreticulate, with a few longitudinal costae along midline, interstices with piligerous punctae, some high-elevation populations with face sculpture more polished and effaced, especially on side of head, which can be smooth and shiny; scape relatively short (SI 83-89), not reaching posterior margin of head when laid back; scape surface mostly smooth and shiny, with scattered piligerous punctae; flagellum with an indistinct 4-segmented antennal club; mesosoma usually densely sculptured, with promesonotum mostly foveate (especially on dorsum) and remaining surfaces foveate to rugoreticulate or rugose, in some high-elevation populations sculpture is reduced, with foveae on promesonotal dorsum appearing more like transverse furrows, and with side of promesonotum largely smooth and shiny; propodeal declivity mostly smooth and shiny, usually with a few transverse carinulae; promesonotum in profile low-domed, slightly asymmetrical, with the apex shifted anteriorly; anterior face of promesonotum longer and steeper than posterior face and mostly smooth; metanotal groove well-demarcated, of moderate width and depth; propodeal spines forming sharp angles or at most small tubercles (PSL 0.12-0.16, PSI 1.0-1.3); petiole relatively long (PL/HW 0.58-0.63), with node of average size (PH/PL 0.51-0.54); node in profile variable, usually forming a small roughly symmetrical dome with a rounded dorsum, but sometimes dome more asymmetrical with anterior face longer than posterior face, and sometimes with apex more sharp and positioned anterior of midpoint; postpetiole somewhat elongate (PPH/PPL 0.79-0.88) and globular, about the same height and volume as petiolar node (PPH/PH 0.88-0.98), postpetiolar node asymmetrical, with anterior face longer than posterior face; venter of postpetiole in profile usually distinctly sinuous, with anteroventral margin forming a small process; petiolar and postpetiolar nodes mostly smooth and shiny, remaining waist surfaces faintly punctate; gaster mostly smooth and shiny, with scattered piligerous punctae; most of body with a moderately dense layer of long suberect to subdecumbent pilosity; scape with layer of longer sparser suberect setae and layer of shorter subdecumbent setae; gastral setae not distinctly bilayered, forming a moderately dense layer of long suberect to subdecumbent setae; setae on legs suberect to decumbent, with longer suberect hairs on coxae and femoral venters.  , FLI 33-35 (34), PSI 1.1-1.2 (1.1), MFI 92-94 (94), ACI1 65-67 (65), ACI2 83-89 (86).
Same as worker except for standard queen modifications and the following: mesoscutum foveate, except for a longitudinal strip of completely smooth cuticle, which crosses the entire surface; mesopleuron mostly smooth and shiny; propodeum carinate to rugose, with sculpture transversely wrapping around surface; wing venation as in Figure 171D.
Male. Unknown. Biology. Stenamma zelum is known almost exclusively from Winkler and Berlese samples of sifted leaf litter. Only once has a stray individual (a dealate queen) been collected by general searching. This species is found from 350-1700 m elevation, but is most common at mid-elevations around 1000 m. It inhabits mature wet forest environments, such as montane rainforest and cloud forest.
Comments. Stenamma zelum is a very distinctive species, unlikely to be confused with anything else. The only exception being S. brujita, which is not closely related, but has many convergent traits (e.g. size and sculpture). Separation of these two species is discussed in detail in the comments section under S. brujita, but I will restate here that these species have not been collected in sympatry, and should be easy to separate using locality data alone.
Molecular phylogenetic results indicate that S. zelum is sister to the expolitum species group, which includes S. alas, S. expolitico, and S. expolitum (Branstetter 2012). However, S. zelum is distinct from these species and shares none of the diagnostic morphological character states of the species group.
Within my concept of S. zelum, there are two morphotypes, the more common form, represented by the type series (Figure 169), and a high elevation form (variant 1; Figure 170), which is known only from a few sites above 1500 m in Costa Rica (e.g. 9km NE Vara Blanca, Est. Pittier, Las Alturas Biological Station). The variant has reduced sculpturing, in which the foveae have become less distinct, and large smooth patches are present on the side of the head and pronotum. Also, the clypeal teeth are reduced, with the inner teeth blunt and nearly absent.
Preliminary molecular phylogenetic results, which include several populations of each morphotype, show that the two forms separate into sister clades, suggesting that the high-elevation variant may represent a distinct species. However, I choose to recognize one species until variation within the high-elevation form is better understood.