282 ERNEST A. BACK. 



Cyrtopogon leucozonus. 



Cyrtopogon leucozonus Loew, Berl. Ent. Zeit., 1874, 364. 

 Cyrtopogon leucozonus Osten Sacken, West. Dipt., 299, 1877 

 (translation) . 



° . — Length 8-9 mm. — Black; posterior tibia? and their metatarsi 

 reddish, with black and white pile, abdomen wholly white pilose, seg- 

 ments 2-5 each adorned with a posterior white pruinose fascia; wings 

 grayish hyaline. 



Deep black; hind tibiae, and the middle ones in a much less degree, 

 reddish, their extreme bases brown, their tips hardly darkened; 

 hind metatarsi dark reddish, brownish toward tip. Face, front and 

 occiput grayish-white pruinose. The dense mystax reaching to an- 

 tennas, black, white above. Antennas black. Pile of front long, black; 

 that of the palpi, upper occiput and a narrow fringe along the occipital 

 orbits likewise black; that of the rest of the occiput and basal segments 

 of antennae, white. Dorsum whitish-gray pruinose near the humeri, 

 elsewhere brownish-gray pruinose, the markings of dorsum very in- 

 distinct; pile chiefly white, but from the middle toward the anterior 

 margin, the black hairs become gradually more numerous; usual thor- 

 acic bristles black. Pleura? brownish-gray pruinose, pile wholly white; 

 that on the mesopleura and before the halteres well developed. Scutel- 

 lum everywhere thinly clothed with long black and white hairs mixed. 

 Halteres whitish-yellow with brown stem. Abdomen polished black; 

 segments 2-5 each with a moderately broad white pruinose cross-band, 

 that on segment 5 interrupted; pile of abdomen wholly white, longer 

 at base, shorter and more scarce toward the end. Pile of coxae wholly 

 white. Pile of femora prevailingly, but not exclusively, whitish; that 

 of anterior femora toward tip mostly black on the upper and anterior 

 side; on the posterior femora most of the black pile is at the end of 

 their posterior side. Hairs of front and middle tibiae mostly black, on 

 the upper side of the latter numerous white hairs are mixed with the 

 black; on the posterior tibiae the under side is beset with long black 

 hairs, while the rest of the pile is white, on the upper side rather dense 

 and moderately long; pile of tarsi and bristles of legs black. Wings 

 grayish hyaline, hardly more grayish on distal half; venation normal, 

 veins blackish, the central cross-veins show in their immediate sur- 

 roundings distinct traces of a darker shade, which are probably less 

 distinct in very fresh specimens. 



Type. — There are five females in Osten Sacken's collection 

 at the M. C. Z. Whether one of these is Loew's type is hard 

 to say. 



Habitat. — Sierra Nevada (type), Webber Lake (July 22), 

 and Yosemite Valley (June 8), Cal.; Beulah, N. M. (H. 

 Skinner) . 



