496 



patches posterior to it ; fifth segment with two small but conspicuous 

 groups of black setulse near base, and many weaker setulae on dorsum. 



Imago; Male. — Differs from tenuis in being a little more distinctly 

 vittate. 



Structurally the male is distinguishable from tenuis by the shorter 

 basal joint of the tarsi, the proportions of tibiae and tarsi being 30, 18. 

 In other respects the two species are very similar. 



Female. — Pale yellow. Mesonotum without vittse. 



Agrees with the male except in sexual characters and in having 

 the cross vein slightly nearer to base of wing. 



Length, 1.5-2 mm. 



Illinois localities: Momence, July 17, 19 14 (C. A. Hart) ; and the 

 Illinois River at Havana (larvae and pupse). 



Originally described from Ithaca, N. Y. I have before me one 

 male specimen from the type locality, and two others of this sex from 

 Moscow, Idaho, the former submitted by Professor Johannsen, and 

 the latter by Professor Aldrich. 



15. Tanytarsus dubius, n. sp. 



Male. — Agrees in color with politiis except that the abdomen is 

 usually bright green. 



Structurally also there is a striking similarity to poUtits, the prin- 

 cipal distinctions being in the comparative lengths of the basal joints 

 of the fore tarsi and the fore tibiae. In the present species the basal 

 joint of the tarsi is distinctly more than one half longer than the tibise 

 (40: 25), while in politus it is slightly less than this. The hypopygia 

 of the two species are so similar in general appearance that they are of 

 little service as a means of differentiation, both being very similar to 

 the hypopygium of dives. The distance from base of first vein to. 

 cross vein in the present species is distinctly less than the distance 

 from the cross vein to apex of wing (35 : 46), and the cubitus forks 

 slightly beyond the cross vein. 



Female. — Differs from the male only in 'sexual characters and in 

 venation, the cross vein being slightly nearer to base of wing and the 

 cubitus forking more distinctly beyond the cross vein. 



Length, 2.5-3.5 mm. 



Type locality, Havana, 111., along shore of Illinois River, April 

 28-29, 19 14 (C. A. Hart and J. R. Malloch). 



