252 ERNEST A. BACK. 



Slender black species with face, and often the front, brassy yellow 

 pruinose, the occiput with grayish bloom, particularly prominent along 

 the orbits; mystax confined wholly to the oral margin black; black 

 also is the rather long pile of the basal segments of antennae, frontal 

 orbits, ocellar tubercle and occiput; the scanty beard and pile of the 

 black proboscis and palpi white. Antennae black; segments 1 and 2 

 subequal, cylindrical, the second somewhat incrassate at tip; segment 

 .3 spindle-shaped, a trifle longer than segments 1 and 2 taken together; 

 style very short, sometimes pointed; often blunt. Thoracic dorsum 

 clothed with light golden pubescence which is much more dense on 

 the sides than elsewhere; bristles weak, black; pleurae polished; on 

 the mesopleurae just below the dorsopleurae suture with golden pubes- 

 cence on sides of prothorax, posterior portion of the sternopleurae and 

 above the posterior coxae; trichostical pile fine, pale yellow. Scutellum 

 bare, polished. Halteres whitish-yellow. Abdomen slender, polished 

 black, with coppery reflections; segments 1 and 2 on the sides with fine 

 pale golden or white pile, rest of abdomen with very sparse microscopic 

 pale yellow pile, which in several California specimens is more pro- 

 nounced, but never at all obscuring the ground color. Legs black, 

 though slightly variable; the coxae white pruinose and white pilose; 

 all the femora below with minute denticles and thicker white pile; tibiae 

 and tarsi with scant pile and bristles; claws black; pul villi tawny. 

 Wings faintly blackish hyaline, the basal portion in the male very apt 

 to be whitish; all the posterior cells broadly, and the anal cell nar- 

 rowly, open. 



Type. — British Museum. 



Habitat. — White Mts., N. H., and Catskill Mts. and the 

 Pahsades, N. Y. (Osten Sacken) ; Amherst, Mass. (June 13 

 and July 28) ; Conn. ; N. J. (July 19, 20, 24, 29, 30; E. Daecke) ; 

 Montg. Co., Pa. (May 30, C. W. Johnson); Potomac Cr. (May 

 22), and Dixie Lndg. (June 1), Va.; N. C; Ga.; Fla.; Wash. 

 (S. W. Williston); Cal. (Osten Sacken). 



In his Western Diptera, Osten Sacken speaks of ten male 

 and female specimens from the White Mts, N. H., Catskill 

 Mts. and the Palisades, N. Y., as follows: — " some of the males 

 have the whole auxiliary region of the wing distinctly whitish, 

 while in others the whitish tinge is very distinct on the whole 

 proximal half of the wing. One of the males from the White 

 Mts. has the proximal two-thirds of the wing pale yellowish, 

 the distal third blackish, the tibiae yellowish-red except at 

 the tip, the fore femora yellowish-red except a broad black 

 stripe on their upper surface. The Californian specimens show 



