214 ERNEST A. BACK. 



Reddish-brown; face, front, occiput and pleurae densely grayish- 

 white pruinose, the dorsum more thinly, and the abdomen very faintly 

 so; last four segments of the female abdomen and the entire venter 

 in both sexes, except at the base, without bloom and polished. The 

 four setae of the mystax, bristles of the palpi, beard and upper occiput 

 stout and black, as are they elsewhere on the almost bare body; 

 bristles on the posterior callosities pale at tip. Halteres yellowish, 

 stalk darker. Hypopygium more yellowish-red than the rest of the 

 abdomen, with black, sometimes fulvous, hair; spines of the ovipositor 

 crimson. Legs darker than the body, with short stout hair and longer 

 black bristles. Claws black, red at base; pulvilli straw-colored. Wings 

 whitish hyaline, excepting the apical half of the anterior margin, the 

 apical third of the wing and a very broad border on the posterior 

 margin, milky-white; veins yellowish. The milky color in the wings 

 of the female is less widely diffused than in those of the male. 



Type. — M. C. Z. Type series consists of three males and 

 six females. 



Habitat. — Pecos River, Texas; Kansas; N. M. 



Easily separated from the blackish-winged morosum by the 

 milky whiteness of its wings and the even whitish bloom of its 

 head and thorax. 



Micvostylum moro.siiiu (PI. VI, fig. 4 9); (PI. VIII, fig. 4 J>). 



Microstylum morosum Loew, Cent., X, 27, 1872. 



Microstylum pollens Osten Sacken, Aldrich Cat. of N. A. Dipt., 

 256; note. 



Microstylum morosum Howard, Insect Book, 1902; PI. XIX, 

 fig' 17. 

 (^ $ . — Length 35-37 min. — Black, legs and wings of the same color; 

 head and thorax whitish pruinose, the bloom on the dorsum, how- 

 ever, extremely thin except on the margins; bristles of mystax, beard 

 and coxae white. Female abdomen reddish above. 



Face and front densely whitish pruinose, occiput less densely so, 

 e.xcept along the orbits, mystax white, composed of more bristles than 

 in galactodes; the palpi, segments 1 and 2 of antennae, the front and 

 occiput with black bristles and hair; rest of the bristles of the occiput 

 and the beard white. Segment 2 of the antennae reddish. The white 

 bloom of the dorsum, because of its thinness in the center, appears 

 most clearly as a band extending along the sides back to and including 

 the scutellum; pleurae likewise whitish pruinose, but more densely so 

 below the sternopleural suture. Prothorax above with black bristles, 

 below on the sides with whitish pile. Dorsum rather bare, with very 

 short black hair, but on the posterior callosities with dense short 

 whitish pile. Bristles on the posterior callosities, the coxae, before the 



