A new species of smooth skink (Squamata: Scincidae: Scincella) from Cambodia

Based on morphological and genetic evidence we evaluated the taxonomic status of a newly discovered forest-dwelling population of skink (genus Scincella) from the Keo Seima Wildlife Sanctuary, Mondulkiri Province, Cambodia. From phylogenetic analysis of a 668-bp fragment of the mtDNA COI and diagnostic morphological characters we allocate the newly discovered population to the Scincella reevesii–S. rufocaudata species complex and describe it as Scincella nigrofasciata sp. nov. The new skink species can be distinguished from all other Southeast Asian congeners by the following combination of morphological characters: snout-vent length (SVL) 40.0–52.6 mm; relative tail length (TaL/SVL ratio) 1.25–1.94; prefrontals in broad contact; infralabials 6; primary temporals 2; relative forelimb length (FIL/SVL ratio) 0.20–0.22; relative hindlimb length (HIL/SVL ratio) 0.30–0.33; relative forearm length (FoL/SVL ratio) 0.14–0.16; adpressed forelimbs and hind limbs either overlapping (0.4–2.2 mm) or separated (1.9–2.3 mm); midbody scale rows 32–33, paravertebral scales 69–74, vertebral scales 65–69; dorsal scales between dorsolateral stripes 8; comparatively slender fingers and toes, subdigital lamellae under fourth toe 15–17; dark discontinuous regular dorsal stripes 5–7; distinct black dorsolateral stripes, narrowing to lateral sides and extending to 52%–86% of total tail length. We provide additional information on the holotype of Scincella rufocaudata (Darevsky & Nguyen, 1983), and provide evidence for the species status of Scincella rupicola. Our discovery brings the number of Scincella species in Cambodia to five and emphasizes the incompleteness of knowledge on the herpetofaunal diversity of this country.


INTRODUCTION
The family Scincidae is one of the most globally diverse groups of lizards with 146 genera and about 1 650 species currently recognized worldwide (Uetz et al., 2018). Of these, the smooth skink genus Scincella Mittleman, 1950 currently contains 34 species with fragmented distribution, from the North American continent (five species) to Japan, Ryukyu Archipelago and Taiwan, China, Korean Peninsula, mainland China, and Southeast Asia (remaining species) (Ouboter, 1986;Uetz et al., 2018). Scincella species are characterized by their small size, elongated body, short limbs, relatively long tail, smooth subcycloid scales (most species), small oblong head with transparent disc in a movable lower eyelid, absence of supranasals, pentadactyl hindlimbs, one row of basal subdigital lamellae (most species), median preanals overlapping lateral ones, four or more scales bordering the parietals between the upper secondary temporals, and lower secondary temporal overlapping the upper one (diagnosis follows Greer & Shea, 2003;Lim, 1998;Nguyen et al., 2010aNguyen et al., , 2010bNguyen et al., , 2010c. Furthermore, the genus Scincella is differentiated from closely related Sphenomorphus Fitzinger by the presence of a transparent window in the lower eyelid as opposed to lower eyelid covered with polygonal scales in Sphenomorphus (Greer, 1974;Nguyen et al., 2010a).
The phylogenetic relationships of Scincella and many other Southeast Asian lygosomine skinks remain unresolved because they share many morphological similarities (e.g., Nguyen et al., 2010aNguyen et al., , 2010b. Based on examination of museum specimens, Ouboter (1986) undertook a major revision of Scincella Mittleman, 1950, which resulted in numerous synonymies, some of which are discussed in the present paper (see Discussion).
Following recent changes in and transfer of the protected area management from the Ministry of Agriculture, Forestry, and Fisheries to the Ministry of Environment of Cambodia, the Keo Seima Biodiversity Conservation Area was reorganized and renamed as the Keo Seima Wildlife Sanctuary, covering an area of 292 690 hectares and spanning the Mondulkiri and Kratie provinces of south-eastern Cambodia. The sanctuary is located in the Keo Seima, O'Raing, and Senmorom districts in Mondulkiri Province and Snoul District of Kratie Province in Cambodia (Figure 1). Despite its high biodiversity, low level of disturbance, and high percentage of forest cover (Nuttall et al., 2015), little is known about the sanctuary's herpetofauna. Recent herpetological field surveys in Cambodia have focused on the Cardamom Mountains (Grismer et al., 2007(Grismer et al., , 2008Neang et al., 2010Neang et al., , 2015Stuart & Emmett, 2006), with only two undertaken in Mondulkiri Province (Neang & Poyarkov, 2016;. Biogeographically, the hilly areas of the eastern plain of Cambodia are linked to the Annamite Range (or Truong Son Mountains) of Vietnam , where many new herpetofaunal species have been described in recent years (Hartmann et al., 2013;Nazarov et al., 2012;Nguyen et al., 2013;Poyarkov et al., 2014Poyarkov et al., , 2015aPoyarkov et al., , 2015bRowley et al., 2016).
During a field survey at Prey Lang in northern central Cambodia between June and July 2014, 10 specimens were collected and tentatively assigned to Scincella cf. rupicola based on their external morphology (Hayes et al., 2015;see Discussion). During a second herpetofaunal survey between 22 and 28 September 2016 in Keo Seima Wildlife Sanctuary in south-east Cambodia, we recorded nine species of amphibians and 17 species of reptiles. Among these, eight specimens were assigned to the genus Scincella based on their body habitus and external morphology. However, further morphological and molecular analyses indicated that this population represents a yet to be described species of Scincella, which we describe herein.

Sampling
The herpetofauna field survey was undertaken during the day and night between 22 and 28 September 2015 in semi-evergreen forest in Keo Seima Wildlife Sanctuary. Specimens were captured by hand and kept in plastic bags until the next morning. Specimens were photographed prior to euthanasia and subsequent preservation in 10% formalin. Liver tissue samples were taken for molecular analyses prior to preservation in formalin and subsequently stored in 95% ethanol. Upon arrival to the collection, the specimens were washed in water for 12 h, then transferred to 70% ethanol for storage. Specimens were deposited in the Zoological Museum at the Centre for Biodiversity Conservation of the Royal University of Phnom Penh (CBC RUPP). Additionally, we examined the type series, including the holotype specimen of Sphenomorphus rufocaudatus Darevsky & Nguyen, 1983 (ZISP 19797, St. Petersburg, Russia).

Morphological analyses
Characters were observed under a Nikon SMZ 645 dissecting microscope and measured with a digital caliper to the nearest 0.1 mm and ratio to 0.01.
The following morphometric characters were measured: eye diameter (ED) -maximum horizontal diameter of eye; forearm length (FoL) -length between forelimb elbow and tip of fourth finger with limb held at right angle to body; forelimb length (FlL) -length between axilla and tip of fourth finger with limb held at right angle to body; head depth (HD) -maximum height posterior to extremity of eye; head length (HL) -length from tip of snout to posterior margin of parietals; hind limb length (HlL) -length from groin and tip of fourth toe with limb held at right angle to body; head width (HW) -maximum width of head; snout-forelimb length (SFlL) -length from snout to anterior margin of axilla; snout length (SnL) -length from anterior corner of eye to tip of snout; snout-tympanum length (STL) -length from snout to anterior margin of tympanum; snout to vent length (SVL) -length from tip of snout to vent; tail length (TaL) -length from vent to tip of tail; tympanum diameter (TD) -maximum diameter of ear; trunk length (TrunkL) -length from posterior margin of axilla to anterior groin, with limbs held at right angles to body. Scale counts included: supralabials (SL) -number of upper labial scales; infralabials (IL) -number of lower labial scales; temporals including primary temporals -number of scales above posterior supralabial, posterior postsuboculars, and below parietal and secondary temporal; supraciliaries -counted following Ouboter (1986) and Lim (1998); enlarged nuchals (EnLN) -number of enlarged nuchal scales contacting to parietals posteriorly; midbody scale rows (MBSR) -scales around midpoint of trunk; paravertebral scale rows (PVSR) -number of scales from posterior edge of parietals to point opposite vent; dorsal scale rows between dorsolateral stripes (DBR) -number of dorsal scale rows at midbody between dark dorsolateral stripes, following Inger et al. (1990); ventral scales (VS) -number of scales between gulars and preanal scales; subdigital lamellae under fourth finger (SDLF4); subdigital lamellae under fourth toe (SDLT4).

DNA isolation, PCR, and sequencing
For molecular analysis, we examined 22 specimens of Scincella from Cambodia and adjacent areas of Vietnam, with the sequence from Sphenomorphus maculatus used as an outgroup ( Table 2). The geographic locations of the examined populations are shown in Figure 1.
For molecular phylogenetic analyses, total genomic DNA was extracted from ethanol-preserved femoral muscle and liver tissues using standard phenol-chloroform-proteinase K (final concentration 1 mg/mL) extraction, with subsequent isopropanol precipitation (protocols per Hillis et al., 1996 andSambrook et al., 1989). Isolated total genomic DNA was visualized by 1.5% agarose gel electrophoresis in the presence of ethidium bromide. The concentration of total DNA was measured in 1 µL using a NanoDrop 2000 (Thermo Scientific, USA), and consequently adjusted to 100 ng DNA/µL.
We used two primer pairs for PCR and sequencing, depending on their performance in PCR, for different samples.
The PCR products were loaded onto 1.5% agarose gels in the presence of ethidium bromide and visualized by agarose electrophoresis. If distinct bands were produced, products were purified using 2 µL from a 1:4 dilution of ExoSap-It (Amersham, UK) per 5 µL of PCR product prior to cycle sequencing. The 10-µL sequencing reaction included 2 µL of template, 2.5 µL of sequencing buffer, 0.8 µL of 10 pmol primer, 0.4 µL of BigDye Terminator v3.1 Sequencing Standard (Applied Biosystems, USA), and 4.2 µL of water. The cycle sequencing reaction consisted of 35 cycles of 10 s at 96 • C, 10 s at 50 • C, and 4 min at 60 • C. Cycle sequencing products were purified by ethanol precipitation. Sequence data collection and visualization were performed on an ABI 3730xl automated sequencer (Applied Biosystems, USA). The obtained fragments were sequenced in both directions for each sample, and a consensus sequence was generated using SeqMan v5.06 (Burland, 1999). The obtained sequences were deposited in GenBank under accession numbers MH119607-MH119629 (Table 2).

Phylogenetic analyses
The COI dataset subjected to phylogenetic analyses included 22 Scincella representatives from Cambodia and Vietnam and Sphenomorphus maculatus used as an outgroup to Scincella based on Pyron et al. (2013) (Table 2).
Nucleotide sequences were initially aligned using ClustalX 1.81 (Thompson et al., 1997) with default parameters, and then optimized manually in BioEdit 7.0.5.2 (Hall, 1999) and MEGA 7.0 (Kumar et al., 2016). The final alignment included 668 sites. Mean uncorrected genetic distances (P-distances) between sequences were determined with MEGA 7.0. MODELTEST v.3.06 (Posada & Crandall, 1998) was used to estimate the optimal model of DNA evolution. The best-fitting models selected for the COI dataset were SYM+I for the first, F81+I for the second, and HKY+G for the third codon positions, as suggested by the Akaike Information Criterion (AIC).

Genealogical relationships and species identification inferred from COI dataset
The BI and ML analyses showed essentially similar topologies ( Figure 2), differing only slightly from each other in associations at several poorly supported basal nodes. All six examined species of Scincella formed six corresponding clades with high levels of node support (BPP=1.0; MLBS=100%). Abbreviation of character states: in contact (+); male (M), female (F), subadult (SubA); positive values in "Adpressed limbs" correspond to length of overlap between adpressed limbs (in mm); negative values correspond to length of gap separating finger tips of fore-and hindlimbs when adpressed (in mm), L (left); R (right).  The partial COI gene fragment can be applied as a DNA-barcoding marker, but should not be used as a single tool for reconstructing phylogenetic relationships . However, the examined fragment clearly showed that S. reevesii from the Cardamom Mountains in Cambodia, S. rupicola from central Cambodia, S. rufocaudata from central Vietnam, and the newly discovered population of Scincella from Mondulkiri Province formed a well-supported clade (BPP=0.99; MLBS=95%), though phylogenetic relationships within this clade were essentially unresolved. Scincella reevesii from Cardamom Mountains and S. rufocaudata from central Vietnam were phylogenetically close to each other and represented sister species in our analyses ( Figure 2).
There was slight differentiation within S. rupicola, which clustered in two reciprocally monophyletic groups.

Genetic distances
The uncorrected genetic P-distances in the examined COI gene fragments among and within the studied Scincella species are shown in Table 3.
The observed interspecific distances in the COI gene between the examined Scincella species varied from P=8.84% (between S. reevesii and S. rufocaudata) to P=21.58% (between S. rupicola and S. melanosticta) ( Table 3). The observed intraspecific distances in our analysis varied from P=0.16% to P=2.99%, with the latter value corresponding to genetic differentiation between mtDNA lineages of S. rufocaudata (Table 3).

Systematics
The newly discovered population of Scincella from Mondulkiri Province represents an independent mtDNA lineage, with phylogenetic relationships to S. reevesii, S. rufocaudata, and S. rupicola (Figure 2). This population was clearly distinct in COI sequences from all examined congeners with P-distances in interspecific comparisons varying from 13.29% (with S. rufocaudata) to 19.92% (with S. melanosticta) (Table 3), indicating deep divergence in the examined mtDNA marker.
Morphologically the Mondulkiri population of Scincella also showed affinities with S. reevesii and S. rufocaudata; however, it can be easily diagnosed from these species and other congeners inhabiting the Indochina region by several morphological diagnostic characters (see Comparisons below). Herein, we describe this population as a new species. Scincella nigrofasciata sp. nov.    Table 2. Sphenomorphus maculatus was used as an outgroup. Numbers near nodes represent posterior probability (BPP) or bootstrap support values (MLBS, 1 000 replicates) for BI/ML inferences, respectively. Head: Snout rounded in profile and dorsal view, SnL 3.4 mm, more than twice as long as TD (1.5 mm); STL 8.8 mm; SFlL 16.9 mm, comprising about one third of SVL; ear vertically oval, TD 1.5 mm; ED 2.5 mm; diameter of cornea 1.3 mm; rostral broad, (width 1.7 mm), almost three times greater than height (0.6 mm), visible from above, in contact with 1 st SL laterally, nasals and frontonasal posteriorly; supranasals absent; frontonasal broad, subtrapezoidal in shape, anterior side forming almost straight suture (0.6 mm) with rostral, posterior width 1.7 mm, as wide as rostral, little more than twice as wide as length (0.8 mm), in contact with nasals and 1 st loreal laterally, posterior margin slightly overlapping prefrontals; prefrontals in broad contact, laterally bordered by two loreals, frontal posteriorly; frontal elongated (length 2.8 mm), kite-shaped, posterior part much longer than anterior; greatest width anteriorly 1.4 mm, twice as narrow as length (width/length 0.5); frontal in contact with 1 st and 2 nd supraoculars laterally, frontoparietals posteriorly, anterior corner of rostral end slightly separating posterior portions of prefrontals medially, posterior corner of frontal slightly overlapping medial suture between frontoparietals; frontoparietals two, each diamond-shaped, together forming a butterfly-shape with median suture 1.2 mm, in contact with 2 nd , 3 rd , and 4 th supraoculars laterally, interparietal and parietals posteriorly; interparietal rather small, kite-shaped, with posterior portion little longer than anterior, in contact with parietals posteriorly, anterior corner of interparietal acute, slightly intruding into median suture between frontoparietals; parietals large, in contact with each other posteriorly (suture 0.6 mm behind posterior corner of interparietal), narrowly contacting 4 th supraocular and posterior supraciliary scale, in broad contact with upper secondary temporal laterally and four nuchal scales posteriorly. Naris rounded, laterally pierced in nasal scale; nasals in contact with 1 st SL ventrally, frontonasal dorsally, 1 st loreal posteriorly; loreals two, anterior loreal rhomboidal, in contact with 2 nd SL ventrally, frontonasal and prefrontal dorsally, posterior loreal subtrapezoidal, in contact with 2 nd and 3 rd SL ventrally, preocular and upper presubocular posteriorly, prefrontal and anterior supraciliary scale dorsally; preocular one, elongate, triangular, in contact with anterior supraciliary scale dorsally, anterior edge of orbit posteriorly, anterior presubocular ventrally; supraciliaries eight, anterior two largest; supraoculars four, first two contacting frontal, second to third contacting frontoparietal; presuboculars three, posterior-most slightly intruding into suture between 3 rd and 4 th SL, anterior-most triangular, slightly larger than posterior-most presubocular; suboculars two, both contacting 4 th SL, anterior slightly overlapping posterior one, slightly overlapped by lower presubocular, posterior broadly overlapping lower postsubocular, both bordered above by granular scales of lower eyelid; postoculars two; postsuboculars four (left side) and five (right side), lowest slightly intruding between 4 th and 5 th SL, uppermost largest; lower eyelid with distinct transparent disc (window) bordered above by small palpebral scales; supralabials six, 1 st smallest, 4 th located ventral to window of eye, 5 th largest; infralabials six, 1 st smallest, 5 th largest; primary temporals two, lower larger, sub-rhomboid, anteriorly in contact with 3 rd and 4 th postsuboculars, ventrally with 5 th and 6 th SL, posteriorly with lower secondary temporal, upper primary temporal subrhomboid, anteriorly in contact with 1 st and 2 nd postsubocular anteriorly, posteriorly with both secondary temporals; secondary temporals two, lower smaller, overlapping upper, in contact with 6 th SL ventrally, upper secondary temporal about twice as large as lower, in contact with posterior-most postsubocular anteriorly, with parietal dorsally and nuchal scale posteriorly; nuchal scales four, bordering posterior edge of parietals, slightly enlarged in comparison with adjacent posterior scales. Mental rounded, width (1.6 mm) more than twice as wide than long (0.7 mm), in contact with 1 st IL laterally, postmental posteriorly; postmental large, width (2.0 mm) greater than length (1.1 mm), in contact with 1 st and 2 nd IL laterally, 1 st chinshield posteriorly; chinshields in three pairs, 1 st pair in broad contact median with each other, contacting 3 rd IL laterally, 2 nd pair separated by subtriangular gular scale, contacting 4 th IL laterally, 3 rd pair separated medially by three gular scales, in contact with 5 th and 6 th IL laterally and three gular scales posteriorly.

Coloration in life:
In life, the female holotype CBC02546 had the same color as female paratype CBC02840 ( Figure  4). Dorsal surface of head, dorsum, and base of tail dark bronze-brown, side of head between tip of snout and forelimb insertion dark brown; dorsal surface of remaining tail reddish-brown. Dark broken regular dorsal stripes anteriorly and on tail (5) and posteriorly on body (7), formed by series of dark dots or elongated black spots, including wider dark paravertebral stripe; anterior part of dorsum with dorsal stripes formed by series of dots, posterior part of dorsum with dark dot-formed regular dorsal stripes reaching base of tail, continuing with dark stripes on dorsal surface of tail, extending about one-third of tail length; light laterodorsal stripes from behind eye, through temporals, along dorsolateral scale row to lateral sides of tail, and fading at one-third of tail length; large distinct regular black longitudinal dorsolateral stripe on each side of body, covering two to three scale rows, starting as narrow stripe covering about one scale row, running from posterior corner of eye through upper temporals, above tympanum, expanding wider to two scale rows above axilla, running below light dorsolateral stripe, along upper flanks through upper angle of groin to lateral surface of tail, becoming indistinct at posterior lateral tail (∼12 mm from tail tip); body flanks ventrally with whitish-beige longitudinal streaks and dark markings on bluish-brown background; ventrolateral surfaces from below level of eye to axillary region with longitudinal whitish-grey streaks and dark marking on reddish-brown background; lateral surfaces of tail reddish-brown; dorsal surfaces of limbs with irregular dark blotches on dark brown background. Ventral surfaces of head, gular region, body, and limbs uniformly white; ventral surface of tail uniform pinkish-cream. Palmar surfaces of hands and thenar surfaces of feet dark grey. Iris light-grey.

Coloration in preservative:
In preservative, dorsal surfaces of holotype turned dark greyish-brown; wide dorsolateral black stripe remained distinct; head with faint irregular dark spots, pineal ocellus present as single white dot on posterior part of interparietal; sides of head and supralabials with dark mottling; infralabials with dark spots; lateral sides of tail with small dark spots; throat and ventral surface of body and limbs greyish-cream; ventral surface of tail lighter cream; palmar surface of hand, fingers, and toes dark grey (Figure 3, Figure  7D, E, F).

Variation:
Paratypes (Table 1) resemble holotype in most morphometric and meristic characters and coloration. Noteworthy variation is that the holotype has six SL on each side of the head, whereas all paratypes have seven. CBC02545 has two supraoculars on left side, second posterior one larger with clear short suture indicating incomplete fusion of two posterior supraoculars; three supraoculars on right side, third with clear short suture indicating incomplete fusion with fourth posterior-most supraocular; one distinct pair of enlarged nuchal scales (remaining specimens have weakly enlarged nuchals) and first pair of chinshields in narrow contact with each other (vs. in broad contact in other specimens). CBC02545 has four postsuboculars and CBC02840 has five postsuboculars on both sides. Male paratype exhibits greater tail length (97.3 mm) than female holotype and paratypes. All specimens have six nuchal scales posterior to parietals, except subadult CBC02842, which has seven. In life, male shows distinctly more reddish-brown coloration of dorsum, with indistinct mid-dorsal stripe; throat, lower body flanks, ventral surfaces of body, lateral and ventral surfaces of tail in male show distinct reddish-orange coloration ( Figure 4B). In preservative, reddish-orange coloration faded and became paler ( Figure 7D).

Natural history:
The species was recorded from semi-deciduous lowland forests at elevations ca. 400-500 m a.s.l. in Keo Seima Wildlife Sanctuary from the eastern plain of Cambodia. Most specimens were encountered during the day, but juveniles CBC02843-45 were encountered at night among leaf litter. The holotype female CBC02546, paratype male CBC02545, and subadult CBC02841 were spotted moving near rotten logs, female CBC02840 was moving along the ground on the forest floor, and subadult CBC02842 was found under a rotten log. Diet and reproductive biology of the new species remain unknown. The gravid female holotype carried two eggs.

Etymology:
The specific epithet is from the Latin words "niger " for "black" and "fascia" for "band", in reference to the wide black dorsolateral stripes typical for this species.
Distribution: To date known only from the type locality in Keo Seima Wildlife Sanctuary, O'Raing District, Mondulkiri Province, Cambodia at elevations ca. 400-500 m a.s.l.. However, the discovery of this species in adjacent areas of southern Vietnam is highly expected.

Comparisons:
The morphological characters distinguishing the new species from its Southeast Asian congeners are summarized in Table 4.
Morphological comparisons of Scincella species found in Cambodia are given in Table 5 (Bourret, 1937) of Vietnam and Laos by its longer SVL in males (50.2 mm, n=1 vs. 34.2-45.4 mm, n=6), lack of lobules around external ear opening (vs. 2-4 lobules), dark brown dorsum with 5-7 discontinuous regular dark dorsal stripes (vs. silver-grey with a dark vertebral stripe), and distinct wide black dorsolateral stripes (vs. dark brown flanks broken up by light spots).
In both morphometric and meristic characters Scincella nigrofasciata sp. nov.
is most similar to S. reevesii and S. rufocaudata. However, the new species can be distinguished from S. reevesii by slightly shorter forelimbs (FIL/SVL 0.20-0.22 vs. 0.24-0.30), generally shorter hind limbs (HIL/SVL 0.30-0.33 vs. 0.34-0.43), comparatively shorter forearms (FoL/SVL 0.14-0.16 vs. 0.17-0.19, Table  5), adpressed limbs overlapping 0.4-2.2 mm in males and subadult specimens and separated by a distance of 1.9-2.3 mm in females (vs. overlapping 3.9-6.5 mm in both sexes), 5-7 dark discontinuous regular dark dorsal stripes (vs. irregular dark vertebral line and dark dorsal spots), wide distinct black dorsolateral stripes, continuing to lateral sides of tail, Figure 4 (vs. dark dorsolateral stripes less distinct and broken up by light spots and only extending to tail base in both sexes, Figure  6E, D), comparatively more slender fingers and toes ( Figure  5A vs. Figure 5C), and dark brown palmar surfaces of hands and lower surface of fingers and toes, Figure 5A (vs. light grey palmar surfaces of hands, fingers and toes, Figure 5C).

DISCUSSION
Our work clearly demonstrated the new species from Mondulkiri Province to be distinct from other Scincella species known from Cambodia, including S. melanosticta, S. reevesii, S. cf. rufocaudata, and S. rupicola. Data on their morphological differences are summarized in Tables 4-5 and Figures 5-7. As the original description of Sphenomorphus rufocaudatus by Darevsky & Nguyen (1983) was quite short and published only in Russian, we provided additional morphological information (Tables 5 and 6) and photos (Figure 8) of the holotype ZISP 19797.
To facilitate future work on the genus Scincella of Cambodia, we provide the following comparisons between the named species, based on specimen examination and character states taken from the literature (Table 4). Scincella melanosticta can be distinguished from S. reevesii by one primary temporal (vs. two) and greater number of DBR (10 vs. 8). Both male and female S. melanosticta have a dorsum with dense dark spots (dark spots on almost every dorsal scale) and lack conspicuous dorsal stripes (vs. vertebral/irregular lines of dorsal spots in S. reevesii, except some male individuals of S. reevesii, probably in the breeding season, show a reddish brown dorsum that lacks dorsal spots), and distinct dark dorsolateral stripes interrupted by irregular light transverse bars/spots (vs. dark dorsolateral stripes, running along upper flanks and less interrupted by light spots). The bifurcated part of the hemipenis is 56% its total length (n=1) in S. melanosticta (vs. 65%-68%, n=2, in S. reevesii).
Scincella melanosticta can be differentiated from S. rupicola by having one primary temporal (vs. two), greater number of DBR (10 vs. 8), dorsum with dense dark dorsal spots in both sexes (vs. dark blotches with pair of smaller blotches on neck in females only, whereas males lack blotches or have very faint dark dorsolateral stripes), and heavy dark spots on sides of head, extending above axillary region and below dorsolateral stripes along flanks in both sexes in S. melanosticta (vs. dark mottling in females and no dark markings in males in S. rupicola (Figures 6A-C; 7A-C).
Scincella reevesii can be distinguished from S. rupicola by its higher TaL/SVL ratio 1. 57-1.73, n=3 (vs. 1.06-1.53, n=5), dark brown dorsum with small vertebral/irregular dorsal spots (vs. dorsal blotches and pair of smaller blotches on neck only in females), distinct wide dark dorsolateral stripes, running along upper flanks, almost not interrupted by light spots (vs. large dark blotches interrupted by light bars in females), and body slender in males (vs. body in males comparatively thicker in S. rupicola) ( Figure 6A, B, D, E; Figure 7G-H).
Abbreviation of character states: present or in contact (+); absent or not in contact (0); data not available (N/A).
We examined photographs of specimens (FMNH 263355-58) from the Cardamom Mountains of southwest Cambodia, deposited at the Field Museum of Natural History, which were assigned to S. rufocaudata by Stuart & Emmett (2006), and suggest that these specimens appear more like S. reevesii than S. rufocaudata based on their dark dorsolateral stripes, which are more continuous and interrupted by less distinct light spots/bars. Two (CBC01380 and CBC02305) out of seven male specimens from the Cardamom Mountains of southwest Cambodia that we assigned to S. reevesii have prefrontals slightly separated and another male (CBC01379) has prefrontals in narrow contact, which we suggest is a variation within this population of S. reevesii.
We examined photographs of specimens (FMNH 262998-99) collected 3-4 km from the new species type locality in Mondulkiri on the Cambodian eastern plain, which were assigned to S. rufocaudata by . These specimens look different from S. rufocaudata, based on their prefrontals in contact as opposed to prefrontals separated in S. rufocaudata; and differ from S. reevesii in having more distinct wide dark dorsolateral stripes; they also differ from the new species based on their light brown dorsal coloration, and lower edge of dorsolateral stripes more interrupted by irregular light spots. However, because these specimens were inaccessible to us, we suggest retaining the specimens FMNH262997-3001 reported by  from Mondulkiri as Scincella cf. rufocaudata, pending further studies and genetic analyses.
The discovery of a new species of Scincella in Mondulkiri Province brings the named species of Scincella known for Cambodia to five, namely, Scincella nigrofasciata sp. nov., S. melanosticta, S. reevesii, S. cf. rufocaudata, and S. cf. rupicola, adding another species of lizard to the country. The new species seems to be morphologically quite variable; therefore, additional adult specimens and further studies are required to assess morphometric and meristic character variations. To date, Scincella nigrofasciata sp. nov. is known only from the type locality in the Mondulkiri Province of Cambodia. However, it is very likely that the new species inhabits other hilly areas of the southern outcrops of the Annamite Mountains in adjacent areas of Vietnam (e.g., Binh Phuoc, Lam Dong, and Dong Nai Provinces), and thus further morphological and molecular studies are needed to confirm the extent of its distribution in southern Indochina. The discovery of a new species of Scincella indicates that the reptile fauna of Keo Seima Wildlife Sanctuary remains insufficiently studied and future field surveys are needed to assess its herpetodiversity. This study further highlights the importance of taxonomic research and biodiversity assessments for nature conservation.       Abbreviation: Present or in contact (+); absent or not in contact (0); data not available (N/A). *: As the holotype has a broken tail, TaL is given according to the original description (Darevsky & Nguyen, 1983). M: male. For abbreviations, see "Materials and methods".