304 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



ered with dense brown pollen ; the lateral ones are considerably abbre- 

 viated anteriorly ; the intermediate one, seen from the front side, appears 

 entire ; seen from the hind side, it appears bisected by a broad black 

 line ; the region in front of the lateral stripes is covered with a thin 

 white pollen, of which there is also a trace in the intervals between the 

 middle stripe and the lateral ones. These intervals do not show the 

 shining surface of the broad lateral margin of the thoracic dorsum, 

 which is entirely free from pollen ; the inner end of the thoracic suture, 

 on each side, shows a small spot of more dense whitish pollen. The 

 thoracic dorsum is beset with long black pile, which is rather scarce, 

 except on the shining black sides of the dorsum, where it is a little more 

 dense. Among this black pile, there is a shorter and more delicate 

 white pubescence ; it does not exist, however, on the shining black por- 

 tions of the dorsum. The shining black scutellum is rather densely 

 beset with long, exclusively black, pile. Pleurae with a thin grayish 

 pollen ; their pubescence in front of the halteres and of the roots of the 

 wings is altogether black ; above the front coxee, the stronger hairs are 

 black, the more delicate pile whitish. Segments 2-4 of the shining 

 black abdomen have on the hind margin a very broad cross-band of 

 white pollen, which is even expanded in the middle ; a similar cross- 

 band on the fifth* segment is less broad, and a little interrupted in the 

 described specimen (perhaps, in consequence of detrition). The pile 

 on the abdomen is rather long, but becomes gradually shorter toward 

 its end. On the five first segments, it is chiefly white ; however, the 

 sides of the three first segments (exclusive of their posterior corners) 

 bear some black pile, which may show a trace of whitish reflection on 

 the tips of the single hairs only. This black pile reaches down to the 

 venter. From segment 6 to the much developed hypopygium the pile 

 on the abdomen is altogether black. Coxae with whitish pile. The 

 black legs do not show any trace of lighter color; they have the ordi- 

 nary structure. The front tarsi are comparatively long, equaled only 

 by those of C. marginalis and montanus. The hairs on the legs are 

 long, chiefly whitish on the femora. At their tip, however, and on the 

 upper and hind side of the front femora, the hairs are more or less ex- 

 clusively black. On the under side of all the femora, especially toward 

 their base, the hairs have a pale yellowish tinge. The pubescence of the 

 front tibise is chiefly black ; but on their distal half there is a good deal 

 of white pile. On the hind tibiae, the hairs are prevailingly white, 

 although there are many black hairs near the base, on the under side 

 more than on the upper side. The hairs on the tarsi are chiefly white, 

 on the upper side of the three first joints of the hind tarsi compara- 

 tively long, otherwise short. All the bristles tin the legs are black. 

 Halteres blackish-brown. Proximal half of the wings hyaline ; distal 

 half blackish-gray ; venation normal ; veins black. 



u Hab. — San Francisco (H. Edwards).' 7 



I have three males from San Eafael, Marin County, Cal., March 31, 

 * The original has fourth ; evidently a mistake. 



i 



