AMERICAN DIPTERA. 355 



tinct, dull olivaceus, the median stripe narrowly divided and distinctly 

 separated from the lateral stripes by a line of grayish bloom; abdomen 

 when viewed from above yellowish-gray pruinose; when viewed from 

 behind, reddish, the lateral margins and posterior angles of the seg- 

 ments only then appearing yellowish-gray pruinose with a small elong- 

 ate black spot on the side above the grayish bloom. Wings nearly 

 hyaline, toward the apex and posterior margins grayish. 



Face and front pale yellowish-gray pruinose, the occiput more 

 olivaceous with pale bristles. Mystax sordid white; hair of front 

 along the orbits and on vertex, short, pale; ocellar tubercle with two 

 black bristles. Antennse yellowish, the basal segments above with 

 black hair, below, with paler hair. Palpi reddish-yellow, with pale 

 pile; proboscis black, yellowish at base below. Thorax dark chestnut; 

 the pleurae nearly black in places; wholly and densely covered with a 

 dull yellowish-gray bloom. Dorsum with three distinct more or less 

 olivaceous stripes ; the median stripe not at all attenuated behind, 

 narrowly bisected by a pale longitudinal line; the lateral stripes greatly 

 abbreviated at both ends, subinterrupted at the transverse suture; 

 on the median stripe often two black lines, and on the lateral ones two 

 black spots may be seen. Bristles of the prothorax and before the 

 halteres pale; of the dorsum and scutellum black. Abdomen rather 

 slender, in certain lights appearing wholly grayish pruinose, though 

 not always so; when viewed from behind and to one side it appears 

 reddish, and then only the lateral and posterior margins of the seg- 

 ments appear pruinose, and segments 2-6 of the male and segments 

 2-5 of the female, display a small black spot on the anterior half. 

 Last two segments of the female abdomen polished red; the male 

 hypopygium polished red with pale pile. Legs yellowish-brown; tips 

 of tarsi and all the bristles black. Coxs like pleurae, with wholly white 

 bristles. Halteres yellowish. Wings narrow, hyaline, soinetimes 

 slightly tinged with yellow; toward the apex and the posterior margin 

 rather grayish, the narrow borders of the veins running to the pos- 

 terior margin, and the posterior margin itself hyaline and destitute of 

 microscopic pubes; the third and fourth longitudinal veins not bor- 

 dered at the apex. 



Type.—M. C. Z. 



Habitat. — Ks. (type) ; Colorado Springs, Col. (Osten Sacken) ; 

 Col. (Morrison, July 30); 111. (Forbes); Glen, Sioux Co., and 

 Lincoln, Neb. (P. R. Jones). 



As I interpret this species in eight specimens from Colorado, 

 it can be separated from the other species by the more grayish 

 thoracic bloom, the somewhat olivaceous dorsal stripes, and 

 in certain lights the almost uniformly pruinose tergum of 



TRANS. AM. ENT. SOC, XXXV. SEPTEMBER, 1909 



