7. Geostiba (Sibiota) crepusculigena Gusarov, sp. n. (Figs. 169­186)

Type material. Holotype,, UNITED STATES: Tennessee: Cocke Co.: Snake Den Ridge Trail, 9 km S Cosby, 35°44.18'N 83°14.60'W, 1520 m, in forest litter, Picea, Rhododendron, Betula (V.I.Gusarov), 23.ix.2001 (KSEM).

Paratypes: UNITED STATES: Tennessee: Cocke Co.: 20 specimens, same data as the holotype; 10 specimens, ditto but 8 km S Cosby, 35°44.61'N 83°14.00'W, 1470 m, Tsuga, Picea, Rhododendron, Betula (all – KSEM, SPSU).

Diagnosis. Geostiba crepusculigena can be distinguished from other Nearctic species of Geostiba by having small eyes (temple length to eye length ratio 3.0­3.1), pronotal pubescence of type V, reduced wings, short elytra (pronotum length to elytron length ratio 1.3), the presence of two short parallel carinae in the middle of abdominal tergum 7 in front of posterior margin, the shape of the aedeagus (Figs. 174­180, 182­186) and the shape of the spermatheca (Fig. 181).

Geostiba crepusculigena differs from closely related G. nimbicola, G. pluvigena and G. nebuligena in having apex of median lobe with obtuse apical projection (in lateral view) (Figs. 176­177, 102­103, 128­129, 155­156).

Description. Length 1.8­2.3 mm. Body brown to dark brown, antennae brown, legs and mouthparts brownish yellow. Body parallel­sided.

Head as wide as long, surface on disk with fine isodiametric microsculpture, puncturation very fine, distance between punctures equal to 3­4 times their diameter. Temple length to eye length ratio 3.0­3.1. 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 as wide as long, width 0.34­0.40 mm, 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 shorter than pronotum (pronotal length to elytral length ratio 1.3), wider than long (1.5), with fine isodiametric microsculpture and fine asperate puncturation, distance between punctures equals 1­3 times their diameter. Elytral suture behind scutellum slightly raised in both sexes. Wings reduced to short vestiges, shorter than elytra.

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 2­6 times their diameter. Tergum 7 without white edge.

Male tergum 7 with two medial carinae in front of posterior margin. Male tergum 8 with two or four weak and short carinae in front of posterior margin, posterior margin convex (Fig. 169). Male sternum 8 with convex posterior margin (Fig. 170).

Female tergum 8 with convex posterior margin (Fig. 171), sternum 8 with strongly emarginate posterior margin (Figs. 172­173).

Aedeagus as in Figs. 174­180, 182­186. Apex of median lobe in ventral view narrow, its outline convex apically (Figs. 174­175), in lateral view strait, with strong obtuse apical projection ventrally (Figs. 176­177), distal diverticula of internal sac in ventral view broad (Figs. 179­180).

Spermatheca as in Fig. 181.

Distribution. Known from Snake Den Mountain in the Great Smoky Mountains massif (Tennessee) (Figs. 338, 340).

Natural History. Geostiba nebuligena was collected at altitudes of 1400­1600 m in leaf litter in mixed forest with red spruce (Picea rubens), birch, purple laurel (Rhododendron catawbiense) and hemlock.

Etymology. The specific name is derived from the Latin noun crepusculum (dusk, twilight) and the verb gigno (to be born, to arise). It refers to the dark forests in the Great Smoky Mountains where the species occurs.