PKOSIMULIUM. 17 



3. Furcation of radial vein very short and ill-defined; mesopleurae 



bare pecuarum, p. 21. 



Furcation of radial vein distinct and elongate; mesopleurae with dis- 

 tinct hairs plcumle, p. 17. 



4. Yellow si)ecies fulvuni, p. 18. 



Black species with gray or j'ellow legs 5 



5. Fork of radius Ions and distinct hiriipes, p. IS. 



Radius unforked niutatum, p. 20. 



6. Entirely j-ellow species fulvum, p. 18. 



Black species 7 



7. Fork of radial vein very short, indistinct pecuarum, p. 21. 



Fork of radial vein long and distinct - hirtipcs, p. IS. 



Prosimulium pleurals, new species. 



Female. — Black-gray, opaque. Frons and face whitish-dusted, 

 antenna^ brown-bhick, palpi concolorous. Mesonotum without stripes 

 or distinct pollinose spots; pleurce, scutellum, and postscutum con- 

 colorous with disk of scutum. Abdomen opaque, black-gray. Legs 

 brownish-yellow; all tarsi, and especially fore pair, and apices of 

 tibiae darkened. Wings grayish, veins brown, thin veins rather 

 more distinct than usual. Halteres brownish-yellow. 



Frons divergent-sided, at vertex twice as wide as at above antenna?, 

 surface thickly covered with long, soft, white hairs; face as long as 

 frons and distinctly longer than broad, colored as frons and similarly 

 haired; antennal pile white, hairs on palpi brown, postocular cilia 

 pale, some longer brown hairs present near eye margins. Mesonotum 

 with long, loose, hairlike, white pilosity, which is longer on the an- 

 terior lateral angles and posteriori}' ; a few longer, dark, upright hairs 

 on posterior fourth; pleural tuft white, extending almost to the lower 

 angle of the epimerum; another group of similarly colored hairs oc- 

 cupying the lower portion of episternum (eps.) ; postspiracular area 

 pale-haired; scutellum with long, white, upright hairs and decum- 

 bent white pilosity. Abdominal basal scale brownish-yellow, the 

 fringe whitish, sides of all segments with long, silk}-, white hairs, 

 disk with much shorter brown hairs. Legs long, with white hairs 

 and shorter white pilosity; hind tarsi with basal two joints of the 

 usual form in this genus; claws bifid (PI. II. fig. 16). "Wings with 

 costal divisions beyond subcostal vein 2:^:11; A'eins fine and short- 

 haired ; basal wing hairs short, brown. 



Length, 4 mm. 



Ti/pe. — Cat. No. 15403. U. S. National Museum. One female, 

 Kaslo, British Columbia (R. P. Currie). 



The early stages are unknown. The situation of the anterior 

 pleural hairs, bifid claws, and furcate radius should readily dis- 

 tinguish this species from any other. 



10125"— 14 2 



