174 



Jewett: Plecoptera 



Fig. 6:37. Terminal abdominal structures of Arcynopteryx. 

 a, picr/'ceps, lateral view of male terminalia; b, yosemite, hook 

 on tenth tergite of male; c, picti'ceps, ventral view of female 

 terminalia; d, aurea, ventral view of female terminalia; e, paral- 

 lela, ventral view of female terminalia; f, dorsal view of male 

 terminalia; g, aureo, lateral view of male terminojia (a, Ricker, 

 1943; b, Needham and Claassen, 1925; c.c^g, Hanson, 1942; 

 e, Frison, 1937; f, Frison, 1936). 



denticles absent from the cusps of the nymphal mandi- 

 ble, or a very few present on the outer left cusp only; 

 Holarctic; northern North America, Colorado, New 



Hampshire Arcynopteryx, s.s. Klapalek 1904 



— Male supra-anal process blunt, not unusually long (fig. 

 6:37/); denticles numerous along both sides of the 

 outer cusps of both mandibles; British Columbia to 



Oregon and California; Montana, and Utah 



(subgenus Skwala Ricker 1943) parallela (Frison) 1936 



Key to the North American Subgenera and 



California Species of Isogenus 



Males 



1. Arms of the mesosternal Y-ridge meet the anterior 

 corners of the furcal pits (indistinct in males of Cher- 



nokrilus ) 2 



— Arms of the mesosternal Y-ridge meet or approach the 



"Adapted from Ricker (1952). See text for Isogenus sorptus 

 (Needham and Claassen). 



posterior corners of the furcal pits 4 I 



Wings almost clear; male lateral stylets short with 

 2 or 3 terminal spinules (figs. 6:38e; ? 6:39a); Washing-; 



ton to California 



(subgenus Osobenus Ricker 1952) yakimae (Hoppe) 193S 

 Wings dark brown; male lateral stylets long, smoothly 



rounded 



(subgenus Chernokrilus Ricker 1952) (in part) 3 



Supra-anal process bluntly hooked at the tip (fig. 6:38A); 



Fieldbrook, California (synonym: Perla venosa 



Needham and Claassen 1925) erratus (Claassen) 1936 

 Supra-anal process straight at the tip (fig. 6:38t; §, 

 6:38<i); Oregon (synonym: Perla obscura 



Fiq. 6:38. Terminal abdominal structures of Isogenus. a,{, 

 nonus; b, c, pilatus; d,i, misnomus; e, yakimae; g, fosronus; 

 b, erratus; a,c,d, ventral view of female terminalio; b,e,r",h,i, 

 dorsal view of male terminalia; g, supra-anal process of male, 

 lateral view; (o, Needham and Claassen, 1925; b,c, Frison, 

 1942b; d,h,i, Ricker, 1952; e, Hoppe, 1938; (, Claassen, 1937b, 

 g, Ricker, 1943). 



