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Dorsal process of abdominal segment 1 barely visible, represented by 

 an elevation without setae. Primary and secondary dorsal setae of seg- 

 ment 9 situated on reddish sclerotized dots. 



Lateral line on segments 3 — 8. Gills on segments 2 — 7; abdominal 

 segment 2 without lateral, presegmental gills. 



Sclerite of segment 9 pale yellow, with 2 rows of dots on each side at 

 anterior margin; setae black; primary anterior- angle seta longer than 

 medioanal seta; intermediate seta thin, moderately long; lateral seta 

 shorter, not always visible among secondary setae; a dark, thin, moderately 

 long seta situated between medioanal setae, displaced slightly to the left; 

 11 — 17 additional secondary setae. 



Sclerite "b" of anal legs yellowish; setae black; median and neighboring 

 dorsal seta long, thick, lateral seta and seta at median margin shorter and 

 thinner; surface with 4 — 5 thin setae. 



Sclerite "c" yellowish white, with broad, black lateral margin; basal 

 seta small, thin, reddish. 



Claw brown, dark brown apically, with a dorsal denticle; setae reddish. 



Case (Figure 471) of characteristic structure, different from that of 

 other species of Potamophylax described, narrow, made of fine, 

 densely arranged sand grains, sometimes mixed with silt, which gives it 

 a brown color; some cases show boundaries of parts built at different 

 seasons; case slightly curved, narrower anteriorly, and especially pos- 

 teriorly, with slightly flattened ventral surface; anterior opening with 

 dorsal hood; posterior opening with a membrane with a large round hole. 



Pupa. Length 16 — 18 mm. Antennae reaching anal rods in male pupae, 

 abdominal segment 7 in female. Labrum and mandibles as in P. nigri- 

 c o r n i s . 



Wing sheaths reaching to abdominal segment 4. Midlegs natatorial; 

 hind tarsi with sparse setae. 



Gills on segments 2—7, as in larva; segment 2 without lateral, pre- 

 segmental gills. 



Hooks of holding apparatus: IH: 1 - 2; IV: 2 - 3; V: 2-3 +8-12; 

 VI: 2-4; VII: 2-3. 



Anal rods with small light setae, as in P. stellatus. Ventral appen- 

 dages of male genitalia (Figure 472) wide, rounded posteriorly, with a 

 distinct, median basal indentation; penis sheath bifid, shorter than ventral 

 appendages. 



Pupal case attached at anterior end by ligaments of a rough adhesive 

 membrane; sievelike part of lid with a few, large holes; posterior end 

 covered with a membrane with small, flat, sand grains, 2 — 3 large, central 

 holes or one hole with lobate margin. 



Mode of life and habitats. Small, clear brooks with a slow 

 current. Summer species, hatching in late July and August. 



Distribution. Northern, western, and central parts of the European 

 USSR, Eastern Siberia. In addition. Central Europe. 



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