218 THOMAS SAY FOUNDATION 



evenly rounded and very finely spinulose; cerci small, 

 membranous; supra-anal process directed upwards and 

 backwards, the outer sheaths with a dentate margin 

 above; subgenital plate quite narrow, considerably pro- 

 longed, turning up almost at a right angle, ventral lobe 

 about twice as long as wide. 



Female, unknown. 



Holotype, male, April 4, 1898, Seattle, Wash. (Cornell 

 University Collection). 



Nemoura truncata Claassen. 



(Plate 39, figs. 1-3.) 

 1923. Nemoura truncata Claassen Can. Ent., 55:290. 



Male. Length to tip of wings, 7 mm. ; expanse, 12.5 mm. 



General color brown. Head wider than prothorax, uni- 

 formly brown, covered with fine pile; hind ocelli closer 

 to eyes than to each other. Prothorax uniformly brown, 

 somewhat rugulose, wider than long, slightly widened be- 

 hind, angles rather broadly rounded. Legs uniformly pale 

 brown. Wings hyaline; anal field of hind wings large. 

 Gills apparently absent. 



Subanal lobes entire, modified into slender pointed proc- 

 esses which reach to the end of the subgenital plate ; cerci 

 large, chitinized, bent inward at the tip and ending in a 

 sharp point; supra-anal process recurved, closely ap- 

 pressed upon the tergum, much widened toward the tip 

 and above with a small pointed tubercle; subgenital plate 

 arising from about the middle of the ninth sternite, 

 broadly truncate at the tip; ventral lobe small, about 

 twice as long as wide. 



Female, unknown. 



Holotype, male, May 13, 1879, Walden, Mass. (S. Hen- 

 shaw, in the Museum of Comparative Zoology, Cambridge, 

 Mass.). 



Nemoura serrata Claassen. 



(Plate 39, figs. 4-<».) 

 1923. Nemoura serrata Claassen Can. Ent., 55:289. 



Male. Length to tip of wings, 7 mm. ; expanse, 12.5 mm. 



General color dark brown. 



Head wider than prothorax, occiput mottled with darker 

 brown ; hind ocelli nearly twice as close to eyes as to 

 each other. Prothorax wider than long, sides straight, not 

 narrowed behind ; surface moderately rugose ; front 

 angles broadly rounded, hind angles sharp. Legs uni- 

 formly lighter brown. Wings uniformly subhyaline ; anal 

 field of hind wings narrow. Gills apparently absent. 



