primary basodorsal seta situated distally and dorsally, on a dark spot, 

 among the secondary setae; 6—8 thick black long setae ventrally; rows of 

 short or long spinelike setae anterior and posterior to them; 1 or 2 black 



471 setae anteriorly and 2 or 3 setae posteriorly, in addition to spinelike brown 

 setae. 



Mid-tibia ventrally with an anterior row of 4 long black setae and 2 shorter 

 light setae and a posterior row of 7 spinules, which are longer apically; 

 thin sparse setae and a curved distal seta and a straight light seta in the 

 middle of the dorsal side; the latter seta longer than the others; posterior 

 primary seta dark brown, distinct, situated subventrally near the apex. 

 Tibia of hind legs longer than tibia of midlegs; it bears numerous soft 

 long thin setae on the dorsal side which are small and light anteriorly; 

 there are also several subventral setae which are strong, brown and 

 spinelike; small subdorsal setae posteriorly; other surface with large 

 covering setae; ventral setae long and black. 



472 Fore and mid-tarsus with sparse, light setae dorsally, with a dark 

 (primary) distodorsal seta and a short, light seta; small covering setae 

 anteriorly and posteriorly; 2 rows of short brown spinules ventrally. Hind 

 tarsi dorsally with numerous, thin, light setae and 2 primary distodorsal 

 long, blackish brown setae; anterior surface with light covering setae; 

 posterior surface with sparser spinelike setae; distal half ventrally with 

 small setae in 2 irregular rows; these setae form strong brown spines, 

 which are longer apically. 



Claw strong, dark brown; basal seta forming a massive spine. 



Abdomen uniformly broad from segment 1 to segment 4, tapering 

 posteriorly from segment 5; segment 9 narrow, small. Small covering 

 setae dark, curved; among them sparse, straight setae, with irregular, 

 apparently broken ends. Primary setae thin, relatively short. A pattern 

 of white, bare stripes and spots among the covering setae. 



Gills of segments 1—8 arranged in 4 rows, 2 pleural rows and 2 ventral 

 rows (Figure 672); gills of pleural rows situated dorsally and ventrally to 

 the white lateral stripe; postsegmental gills situated dorsally to the stripe; 

 gills in middle of the segment ventrally to the stripe. Number of filaments 

 on the gills in the ventrolateral row the largest. Distribution of gills and 

 the number of filaments given in Table 11.* 



Medioanal gills on the metathorax situated close together. 



Primary dorsal setae thin, short, light yellow; anterior-angle setae 

 slightly longer and thicker than the others, restricted to the end of the 

 transverse white stripe, situated in about the middle of the segment; 

 anterior-margin setae small, distinguished with difficulty from the light 

 setae on the segment; relatively large medioanal seta slightly shorter than 

 anterior-angle setae; other 2 surface setae near it thin and light; these 

 setae dark on segment 8, and lateral seta as long and as thick as median seta. 



Ventral side of segments 1—8 with a small dark seta (one of the primary 

 setae) near the base of the gills; segments 7 and 8 without median gills, 

 with a small, light plate near the posterior margin, which is larger on s 

 segment 8 and posteriorly surrounded by massive brown covering setae; 

 a strong brown seta near posterior margin of plate of segment 7; segment 8 

 with 3, sometimes 4—6 such setae. 



* According to counts from specimens from Karelia, Pechora, Bia and Yenisei rivers; higher figures are given 

 by Siltala for larvae from Finland (1905:113). 



537 



