segments 1—2 larger than following segments, each with several setules. 

 Of 3 brown setae on anteclypeus, intermediate seta longer than others, lateral 

 seta shorter (Figure 580, A); 2 — 3 additional setules sometimes present 

 (Nielsen, 1942:615); 5 other setae situated in anterior angle, thick, hooked at 

 end, including 3 moderately long, black, lateral setae and 2 brown, much 

 shorter, median setae. Median blade of mandibles almost straight, with 

 minute, light denticles (Figure 580, B); lateral setae situated basally, brown, 

 ventral seta shorter than dorsal. 



Sheaths of fore wings reaching segment 6 or middle of segment 7, sheaths 

 of hind wings shorter. 



Holding processes of abdominal segment 1 blackish brown, widely 

 separated. Presegmental plates brown, with large denticles, postsegmental 

 plates of segment 5 with small denticles; number of denticles: 111:1—4; 

 IV:l-4; V:2-4 + 10-18; VI:2-4; VII:2-4. Lateral line on segments 5-8 

 is a row of setae with a gap in middle on ventral side of segment 8. 



Anal rods (Figure 580, C) very thin, slightly wider basally, with hook- 

 shaped, inward-curved apex. Sheath of genital appendages of male pupae 

 broadly rounded; penis sheath concave at apex, shorter (Figure 580, D). 



Case 7.5— 9.0 mm long, with 3 small stones on each side; anterior end 

 covered by a small stone attached to case by a sievelike, membranous band 

 with numerous small openings (Figure 580, E); posterior end closed by a 

 dark membrane with 4—9 irregular holes at ventral margin (Figure 580, F). 

 Case attached to lower side of a stone by disks at both ends. 



Mode of life and habitats. On stony bottom, in brooks and 

 rivulets with a more or less rapid current; often in springs and spring-fed 

 brooks. 



Distribution. Central, western, and northern parts of the European 

 USSR. In addition, Europe. 



340 2. Silo proximus Martynov 

 Martynov, 192 6:40. 



Full-grown larva. Length 7.0— 7.5 mm. Head (Figure 581) nnainly dark 

 reddish brown, with large, dorsal, median flat area, as in G. sajanensis. 

 Frontoclypeus brown anteriorly, its entire surface covered with flat tubercles 

 which may resemble a mushroom with a short light stalk and a dark disk • 

 concave in middle and with wide margin; sclerite surface raised into a 

 narrow, dark, tuberculate, transverse keel, which divides anterior from middle 

 part; middle with large, flat tiibercles; posterior part relatively smooth, 

 with minute, dot- shaped tubercles, its anterior and lateral borders formed by 

 a sharp, blackish brown, keel-shaped fold along sutures; a relatively smooth, 

 punctate area bordered by 3—4 blackish brown folds which merge laterally 

 with rows of large, flat tubercles lateral to frontal sutures. Ventral surface 

 yellowish, with reticulate striation in its greater part, middle with a light 

 brown spot, median submarginal area also slightly dark; a large, smooth area 

 with large, pale dots near occipital foramen. Gula triangular, yellowish 

 brown, with indistinct posterior margin; pregula brown, divided by a reddish 

 stripe from gula, its anterior margin with a shallow, median indentation. 

 Chaetotaxy as in S. pall i pes; median and intermediate anterior-margin 



425 



