Number and arrangement o 



f gills of A. 



b s c u r a t a 





Segment 



Dorsal 



Pleural 



Ventral 



2 



1 



1 







1 





3 



1 

 1 



1 



1 





4 



1 

 1 



1 



1 (0) 





5 



1 



1 









6 





 1 









7 











Sclerite "b" brown, basally with large dots, dark margin, with a dark 

 reddish stripe ventrally; setae dark brown; medioanal and neighboring seta 

 thick, long, the former slightly larger; lateral seta strong, moderately long; 

 subapical seta at median margin the same; apical ventral seta short, strong, 

 thin; surface with 6—7 short, small, thin setae. 



Sclerite "c" yellowish brown, with reddish black lateral margin and a 

 small, light seta. 



Claw mainly yellowish brown, blunt, chestnut brown apically, with a large 

 dorsal denticle; seta 1 short, strong, situated subdorsally on median side in 

 basal part; seta 3 situated dorsally, moderately long, but longest on the claw; 

 both setae dark brown, darker and thicker than the 2 setae following; seta 2 

 situated dorsally near end of suture; seta 6 situated near seta 2, short, 

 strong, both setae brown; ventral setae 7 and 8 pale yellowish; seta 5, 

 situated laterally near 8, transparent, small; seta 4 situated subventrally, 

 small, thin, brownish, medial to seta 5 at some distance on membrane of 

 suture. 



Case 14—16 mm long, sometimes 18—19 mm, straight, slightly narrower 

 posteriorly, made of various kinds of detritus, usually pieces of soft, light, 

 debris of trees, with sticks or conifer needles at posterior end, rarely 

 anteriorly; small, flat, particles of mica sometimes among detritus 

 (Figure 538). 



Mode of life and habitats. Clear mountain brooks and rivulets, 

 oligotrophic lakes, especially near river mouths, on solid bottom, usually 

 among sparse vegetation. The species is known from Lake Teletskoe and 

 its tributaries (Samysh, Kamga, Chechenek); and from lakes Taimen'e and 

 Multinskoe in central Altai. 



Distribution. Northern part of the European USSR, Altai, Sayans. 

 In addition. Northern and parts of Central Europe (mainly highlands). 



386 



