plates, and a row of hooks at postei'ior margin of segment 5; number of 

 spinules: 111:5-9; IV:5-8; V:3-9+ 19-27; VI:2-10; VII:4-11. 



Lateral line on segments 5—8. 



Gills as in larva, dorsal, pleural, and ventral; dorsal postsegmental 

 (intei-segmental) gills of segments 2—4 small, with 3—6 filaments; pleural 

 and ventral gills with a single filament on segments 2—6. 



Anal segment narrower posteriorly; anal rods small, thin, curved upward. 



Pupal case dark brown, tetrahedral, 9—12 mm long, sometimes made in 

 part or entii'ely of secretion; edges rounded, sometimes absent, so that 

 cross section is round. Anterior and posterior openings with a brown 

 377 membrane with several holes in middle; number of holes very variable, 



8—25 anteriorly, 5—17 in posterior membrane. Case attached at both ends, 

 anteriorly by 2 large disks on thick stalks and several small ligaments, 

 posterior disks smaller, both at ventral side. 



Mode of life and habitats. Calm rivers and rivulets, large 

 rivers (Dnepr-, Don, Volga, Oka, Kama, Ob', Yenisei), close to the bank in the 

 Yenisei, in parts with slow current, mainly in upper and middle reaches, 

 often among vegetation. Larvae feed on microorganisms and detritus 

 carried by the current, which they capture with spinules and setae of the legs 

 held before the mouth. 



Distribution. The European USSR. Siberia, the Amur Region. In 

 addition, Europe, Iran. 



2. Brachycentrus montanus Klapalek 



Klapalek, 1893:55-59, Figures 1-11.- Ulmer, 1903:87.- Lestage, 

 1921:862-871, Figures 309, b, e, k, 310, b, 312, b. 



Number and arrangement of gills of B. mon 

 tanus (after Klapalek) 



Full-grown larva. Length 10—11 mm. Dorsal side of head mainly 

 chestnut brown, in contrast to B. subnubilus; posterior part of fronto- 

 clypeus with 5—6 small, light dots; similar larger dots lateral to frontal 

 sutures and in posterior part. Gula narrow, dark, trapezoidal. Mouth 



parts as in B. s u b n u b i 1 u s; mandibles 

 as in Figure 632 . 



Pronotum with curved transverse 

 ridge, as in B. s u b n u b i 1 u s, brown, 

 slightly darkex" in middle and at anterior 

 margin. 



Tergites of mesonotum dark brown, 

 median tergites larger, with indistinct, 

 light dots; chaetotaxy as in B. subnu- 

 bilus. Tergites of metanotum with a 

 transverse row of 6 dark setae; lateral 

 tergites with a row of setae of different 

 length anteriorly. 



Legs yellowish brown; femora brown 

 at dorsal margin; chaetotaxy, form, and 

 size of segments as in B. subnubilus. 



Segment 



Dorsal 



Ventral 



2 



6 



1 



3 



6 



1 



4 



6 



1 



6 



6 



1 



7 



6 



1 



8 



3 





472 



