387 Sclerite "c" light brownish, with indistinct, reddish brown, lateral 

 mai'gin; seta small, light. 



Claw (Figure 639, B) bi'own, reddish brown apically, with 2 doi-sal 

 denticles and 4—5 small spinules. Seta 1 situated in basal part, short; 



seta 2 dorsal, moderately long, thin, light brown; seta 3 

 brown, relatively long, situated in distal part; seta 6 

 situated laterally, dorsal to suture, thick, smaller; 

 ventral setae 7 and 8 short, thick, light; seta 5 situated 

 near 8, longer but thinner; seta 4 situated medial to 8, 

 small, thin; setae 5 and 4 light. 



Case tetrahedral, made of detritus, straight, slightly 

 tapering posteriorly, rarely consisting entirely of 

 secretion before pupation, edges little marked or 

 absent, cross section round (Figure 640). 



Mode of life and habitats. Clear mountain 

 rivulets and rivers. 



Distribution. USSR: Northern Kazakhstan, 

 Siberia, Altai, Sayans, Sakhalin. In addition, Mongolia. 



3. Genus Oligoplectrum McLachlan 



Full-grown larva. Length 9—11 mm. Head mainly 

 dark, lighter ventrally, with indistinct dots; ridge 

 bordering flat middle of dorsal surface, extending from 

 margin of frontoclypeus to eye, from seta 14 to coronal 

 suture posteriorly, where ridges of both sides meet in 

 a thin, horseshoe- shaped line in posterior part of head. Quia 

 large, trapezoidal, shorter and wider than in Oligo- 

 plecti'odes.. 

 Mesonotum narrower posterioi'ly in area of lateral tergite; median 

 tergite with fewer and smaller setae at posterior mai-gin than in Oligo - ■ 

 plectrodes. 



Mid- and hind coxae dorsally with large, hooked processes at base, in 

 contrast to Oligoplectrodes; mid- and hind femora similar to those 

 of B r a c hy c e n t r u s, with similar ventral spinules and small, light setae 

 dividing spinules into groups. Tarsus with small, distoventral process, in 

 contrast to Ol i g o p 1 e c t r o d e s; pi'ocess of tibia large, as in Oligo- 

 plectrodes. 



Case made of sand grains, 10— 16 mm long, straight, smooth, narrower 

 posterioi'ly, attached at anterior end. 



Mode of life and habitats. Running water; microphagous, 

 living on food carried by water; cases often occurring in large numbers, 

 attached to stones and other objects. 



Distribution. Western border region of the USSR. In addition, 

 Europe, North America. 



i^—- *»g. 



FIGURE 640. Oligo- 

 plectrodes pota- 

 nini Mart. Larval 

 case 



485 



