Number and arrangement of gills ofS. proximus 



Segment 



Dorsal 



Ventral 



2 



- 



- 



3 



1 

 3 



2 

 3 



4 



1 

 3 



2 

 3 



5 



2 

 4 



2 

 3 



6 



3 

 3 



3 

 3 



7 



3 

 3 



3 

 3 



setae. Anterior lateral tei-gite mainly chestnut brown, lighter laterally and 

 at anterior margin, with flat tubercles, its surface with a small, dark, spine- 

 shaped seta, and 2—3 thin, small setae. Posterior lateral tergite with broad, 



black margin at posterior angle, its 

 surface yellowish, covered with small, 

 light tubercles and oblique dark 

 reddish brown streaks; anterior and 

 median margin with dense, dark 

 tubercles. Tergites of metanotum 

 grayish brown, anterior-margin 

 tergites larger than in S. p a 1 1 i p e s, 

 situated close together in middle, 

 tapering laterally. 



Horn short, light brown. 

 Legs yellowish brown, without 

 punctation; chaetotaxy as in 

 S. pallipes. 



Dorsal and lateral processes of 

 abdominal segment 1 as in S.pal- 

 1 i p e s; lateral line from end of 

 segment 3 to end of segment 7. Gills 

 with 1—4 filaments, on segments 3—7; 

 ventral gills longer than dorsal gills. 

 Segment 9 without tergite; setae at posterior margin as in S. pallipes; 

 medioanal and anterior -angle setae thin, blackish, moderately long; 3 setae 

 between medioanal setae, one of them small; 4 setae between medioanal 

 and anterior-angle setae, intermediate seta moderately long; 4 setae on 

 surface, 2 setae lateral to anterior-angle seta. 



Area "b" of anal legs not sclerotized dorsally; ventral and lateral sides 

 with a narrow, pale brownish sclerite at distal margin; median distal seta 

 blackish brown, as in S. pallipes, lighter and thinner than adjacent black, 

 thick, long seta; lateral seta black, shorter, and thinner; subapical median 

 seta thin, moderately long; 2 small, light setae on surface; ventral seta short, 

 dark bi'own, situated lateral to base of sclerite "c." Sclerite "c" whitish 

 yellow, light brownish at distal and lateral margin; lateral margin dark 

 reddish brown, with small, pointed tubercles. 



Claw brown, reddish brown apically, with a doi'sal denticle; setae as in 

 S. pallipes. 



Case 8— 9 mm long, rarely 10.0—11.1 mm, in form of a wide tube made of 

 small sand grains, coarser grains laterally, usually 2—3 on each side; ventral 

 surface smooth, anterior opening truncate, posterior end covered with a 

 membrane with a single dorsal elliptical hole. 



Mode of life and habitats. Mountain brooks and rivulets with 

 stony bottom. 



Distribution. USSR: the Caucasus. In addition, Iran. 



3. Silo nigricornis Pictet* 



Nielsen, 1942:588-615, Figures 160-175.- Baker, 1963:171-174, 

 Figures 1,4.- Br indie, 1964:197. 



" Described after Nielsen (1942:588-615); we have not seen the larva. Data in the literature are not reliable 

 (see Nielsen, loc cit). 



428 



