Number and arrangement of gills of A.majuscula 



Segment 



Dorsal 



Ventral 



i 



1(0) 



1 (0) 



2 



2(1) 

 1 



1 



3 



1(0) 

 1 



1 



4 



1(0) 



1 



1 



5 



1(0) 



1 



6 





1 



Tergite of abdominal seginent 9 chestnut brown, with 2—3 large, indistinct 

 dots laterally on anterior margin; medioanal setae blackish brown, thicker 

 and slightly longer than anterior -angle setae; 3—4 setae between medioanal 

 setae; 3—4 setae on tergite surface; a small, thin seta lateral to the 

 anterior -angle seta (Figure 218). 



Sclerite "b" of anal legs dark chestnut brown, dark brown on the ventro- 

 distal side, its surface with large brownish dots, with dense scale-shaped 

 tubercles, dorsally, minute spinules at margin. Median distal seta thick, 

 black, long; neighboring seta shorter and thinner; lateral seta thin, 

 moderately long; both reddish brown; a thin, light brown seta subapically 

 near median margin; a short seta on the surface. Sclerite "c" light brown, 

 with very broad, dark reddish brown lateral margin; basal seta small, thick, 

 light. Claw brown proximally, with reddish brown basal margin; apical part 

 dark brown, with thick, dark reddish brown apex; seta 1 short, thick, situated 

 on median side of basal part; seta 3 light, moderately long, situated in distal 

 part; seta 2 large, light, situated subdorsally on the outer side; seta 6 thin, 

 brown, short, situated subdorsally and laterally near end of suture; ventral 

 basal setae 7 and 8 light, situated on membrane near margin; seta 5 small, 

 light, situated distally nearby; seta 4 slightly larger, situated medially. 



Case 10—11 mm long, conical, slightly curved, with smooth walls made 

 of small sand grains; several larger sand grains laterally in anterior part 

 (Figure 219); posterior end covered by a brown membrane with a large 

 hole. 



Mode of life and habitats. Usually in running water, in small, 

 mountain tributaries of Lake Baikal, at a depth of a few centimeters; in 

 the Angara at a depth of 1.0—1.5 m, rarely to 4 m, sometimes in the littoral 

 of spring-fed lakes; in bays and creeks of Baikal Area; on stony bottom 

 with boulders, pebbles, small rock deposits, rarely on sand with some 

 admixture of silt; phytophagous. 



Distribution. Northern part of the European USSR (Arkhangel'sk 

 Region, isolated records (McLachlan, 1874—1880:214); Eastern Siberia; 

 widely distributed in the Yenisei basin, particularly in the Baikal Area, and 

 near Khabarovsk. 



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