Geostiba (Sibiota) silvigena Gusarov, sp. n.

14. Geostiba (Sibiota) silvigena Gusarov, sp. n. (Figs. 321­335)

Type material. Holotype,, UNITED STATES: California: Mendocino Co.: Mendocino [39°18'28"N 123°47'53"W], ex moss in bed of dried up woodland pool, Berlese funnel (J.R.Helfer), 1.x.1954 (CNCI).

Diagnosis. Geostiba silvigena can be distinguished from other Nearctic species of Geostiba by having large eyes (temple length to eye length ratio 2.3), pronotal pubescence of type V, well developed wings, long elytra (pronotum length to elytron length ratio 1.0), the presence of two short parallel carinae in the middle of male abdominal tergum 7 in front of posterior margin, and the shape of the aedeagus (Figs. 323­335).

Geostiba silvigena is very similar to eastern Nearctic G. appalachigena, and differs only in having the apex of median lobe less bent ventrally (in lateral view) (Figs. 325­326, 36­37), and longer and more narrow apex of paramere (Figs. 334, 50).

Geostiba silvigena differs from G. impressula, another western Nearctic species, in having pronotal pubescence of type V, well developed wings, longer elytra, aedeagus with more narrow apex of the median lobe (in ventral view) (Figs. 323­324, 310­312, 315), elytral suture slightly raised behind scutellum, and in males lacking the medial pronotal impression.

Description. Length 2.4 mm. Body reddish brown, antennae, legs and mouthparts brownish yellow. Body parallel­sided.

Head as wide as long, surface on disk with fine isodiametric microsculpture, puncturation very fine and weak, distance between punctures equal to 2­3 times their diameter. Temple length to eye length ratio 2.3. Antennal article 2 longer than article 3, article 4 transverse (width to length ratio 1.6), articles 5­10 strongly transverse, last article as long as 9 and 10 combined (as in Fig. 17).

Pronotum slightly transverse, width 0.41 mm, width to length ratio 1.0, wider than head (pronotal width to head width ratio 1.1); microsculpture and puncturation as on head. Pronotal pubescence of type V. Elytra measured from humeral angle longer than pronotum (pronotal length to elytral length ratio 1.0), wider than long (1.3), with weak and fine isodiametric microsculpture and fine, somewhat asperate puncturation, distance between punctures equals 2­3 times their diameter. Elytral suture behind scutellum raised. Wings fully developed.

Abdominal terga with fine microsculpture of transverse meshes, with fine and sparse puncturation, puncturation becoming finer towards abdomen apex, on terga 3­5 distance between punctures equals 3­5 times their diameter. Tergum 7 with white edge.

Male tergum 7 with two medial carinae in front of posterior margin. Male tergum 8 with four small carinae in front of posterior margin, posterior margin slightly convex (Fig. 321). Male sternum 8 with convex posterior margin (Fig. 322).

Aedeagus as in Figs. 323­335. Apex of median lobe in lateral view bent ventrally (Figs. 325­326), distal diverticula of internal sac in ventral view wide (Figs. 329­330).

Female unknown.

Discussion. Geostiba silvigena has fully developed wings and it is probably widespread along the Pacific coast of North America. The species may not be active in summer when most collections in the area have been made (see the above discussion of natural history of G. impressula). Although G. silvigena is closely related to the eastern Nearctic G. appalachigena, the westernmost locality of G. appalachigena is in Wisconsin (Figs. 336­ 337). Considering the gap between the ranges of the two species and the minor difference in male genitalia the separate status of the two seems justified.

Distribution and variability. Known only from Mendocino, California (Fig. 336).

Natural History. The only known specimen of G. silvigena was collected in moss in the bed of a dried up woodland pool.

Etymology. The specific name is derived from the Latin noun silva (forest, woodland) and the verb gigno (to be born, to arise). It refers to the habitat where the species presumably occurs.