250 ERNEST A. BACK. 



cf .$ — Length 11.5-13 mm. — Very similar to for mo s a in struture of 

 body and antenna?, but only moderately polished black; basal portion 

 of tibiae dull reddish, not clear bright yellowish; pile and bristles of 

 entire body, including that of the palpi and tarsi, pale yellow; wings 

 more dusky, and clouded along the veins. 



Black; only moderately polished; base of the hind tibiae and the 

 basal half of the anterior pairs dull reddish. Face and occiput pale 

 golden pubescent; front polished black. Mystax in male golden; in 

 the female, and the pile and bristles on the rest of the body in both 

 sexes very pale yellow, sometimes nearly white. Thoracic dorsum 

 nearly opaque; pubescence and bristles of both dorsum and pleurae 

 as in formosa, only paler and often more prominent. Halteres pale. 

 Abdomen of female more robust than that of the male, as in formosa. 

 Coxae with rather long pale hair, more abundant on the anterior pairs; 

 the pile and bristles of the legs pale. Wings more dusky than in the 

 more clear-winged formosa, all the veins bordered distinctly with 

 fuscous; all the posterior and anal cells open; the second basal, anal, 

 and axillary cells wholly milky white in the male, in the female not so. 



Type. — M. C. Z. The type series consists of two males and 

 nine females. 



Habitat. — Neb. (type) ; Lincoln, West Point, Harlan, and 

 Sioux Counties, Neb. (P. R. Jones); Wyo.; Mont.; S. D.; 

 Pullman, Wash. 



DIOCTRIA. 

 Dioctria Meigen, Illig. Mag., II, 270, 1803. 

 Dioctria Meigen, Syst. Beschr., II, ISO, 1820. 

 Dioctria Macquart, Hist. Nat. Dipt., I, 289, 1834. 

 Dioctria Schiner, Fauna Austr., I, 119, 1862. 

 Dioctria Coq., Can. Ent., XXV, 80, 1893 (synopsis of species). 



Nearly bare, small or rather small species, polished, and 

 often metallic, black. Head clearly broader than high; face 

 flattened, rather broad, bare, slightly protuberant on oral 

 margin to which the mystax is confined ; vertex rather deeply 

 excavated, ocellar tubercle prominent. Antennas approx- 

 imate, elongate, borne upon a protuberance, very slight in 

 some species, but often highly developed (resplendens and 

 several European species) : segments 1 and 2 cylindrical, slen- 

 der, subequal, or segment 1 excelling in length; segment 3 

 usually equalling in length segments 1 and 2 taken together, 

 linear, as in vera, or broader and more rounded at tip as in 

 albius, sometimes densely microscopically pubescent, usually 



