256 



posterior margin v/ith wide, median depression and short lobes; spinules 

 reddish, small, few. 



Lateral line on segments 5 — 8, open ventrally, with dense, blackish 

 setae. Gills, as in larva, same number and on segments 2 — 7. Holding 

 apparatus on segments 3 — 7; number of hooks : III: 2 — 4; IV: 3 — 4; V: 4 — 

 5 + 12-16; VI: 3-5; VII: 2-4. 



Anal lobes (Figure 446) long, straight in their greater part, slightly 

 tapering posteriorly, curved laterally and dorsally at end, reddish brown; 

 setae dark; basal seta larger than others, in contrast to Lirnnophilus; 

 2nd seta similar, situated between 1st and 2nd third of rod; 3rd seta minute, 

 situated at end of 2nd third; 4th seta slightly larger, situated subapically. 



Pupal case 20—22 mm long, resembling larval case; anterior and pos- 

 terior ends rounded, covered with small stones; a coarse, almost black, 

 membrane around an almost circular hole at anterior end, and an irregular 

 hole at posterior end laterally among the stones; a second, inner memibrane 

 with a hole which may be almost in form of a cross slightly deeper at 

 anterior end, a hole of irregular form at posterior end, with lobes pro- 

 jecting from periphery to center; the opposing lobes usually not reaching 

 each other. Anterior end of case attached to substrate. Cases are some- 

 times found in large aggregations. 



Mode of life and habitats. On stones, on open shore of lakes, 

 in brooks and rivulets, often spring-fed, in a moderately rapid current. 



Distribution. The European USSR, Caucasus, Siberia. In addition, 

 mainly Central and Northern Europe. 



2. Potamophylax nigricornis Pictet 



Pictet, 1834:136-137, Plate VI, Figure 4. - Klapalek, 1893:20-23, 

 Figure S^.g. - Struck, 1900: 14-15, Figure 23. - Ostwald, 1901:.106.- 

 Siltala, 1902: 79-83, Figure 18. - Struck, 1903: 101. - Ulmer, 1903: 65. - 

 Siltala, 1904c: 66; 1907: 502. - Ulmer, 1909: 266, Figure 401. - Lestage, 

 1921: 766-773, Figure 271 d, k, m. - Nielsen, 1942: 497 -539, Figures I, 

 3-8, 120-132. 



Full-grown larva. Length 18 — 20 mm. Head 1.8 — 2.0 mm, mainly 

 yellowish brown, eyes on light background; dark areas reddish brown; 

 dots with dark outline. Anterior part of frontoclypeus with indistinct punc- 

 tation; middle slightly dark; posterior part with distinct, wedge-shaped 

 pattern of large dots, those in posterior row partly fused; dorsal surface 

 slightly dark laterally from frontal sutures, except for a light spot behind 

 eye; rows and groups of large dots instead of dorsal and lateral stripes. 

 Ventral side with similar punctation on pale background near occipital 

 foramen, middle with 2—3 more distinct and darker dots on a slightly dark 

 area. Gula light, long. 



Intermediate, anterior-margin seta longer than median seta, which is 

 thinner, lateral seta light, short, procumbent; anterior frontal seta the 

 same, middle frontal seta moderately long, posterior frontal seta small, 

 thin. Seta 9 long, thick, blackish brown; seta 11 small, thin; seta 7 straight, 

 strong, relatively large; seta 10 light, situated near eye; seta 14 slightly 

 larger than 9 (4/5 as long as width of head); seta 13 small, thin; seta 12 



32] 



