100 PROCEEDINGS OF THE NATIONAL MUSEUM. YoL. 62. 
joint; third joint about as long as the first. Palpi black, white pol- 
linose, and white pilose, with black bristles. 
Thorax, pleura, and scutellum black, dense gray pollinose; pile of 
mesonotum mixed white and black, the bristles black; two whitish 
vittae, a faint brown median stripe and pale brown margining the 
white vittae on the outside. Posterior mesonotum and scutellum 
long white pilose, the scutellum with four black bristles. Pleura 
white pilose. Stems of halteres yellowish, the knob black, gray 
pollinose. 
The black ground color of the abdomen entirely concealed by 
whitish gray pollen, the dorsum with long silvery white pile; pile of 
venter shorter and not so dense. Genitalia characteristic in form, 
mostly white pilose, a few black hairs on the hypandrium; the upper 
claspers long and curved. (Fig. 146.) Femora black, gray pollinose, 
white pilose; no bristles on front and middle femora, the bristles of 
legs black; tibiae yellowish except tips; first tarsal joint yellowish at 
base, the other joints black. Wings hyaline, the stigma brown, veins 
black except at base of wing and along costa; cell M-—3 closed; a short 
stump of a vein near the furcation of Ks in the type. 
Female.—Length 10.5 mm. Very nearly like the male. Body 
entirely pollinose and almost wholly gray. (Frons and mesonotum 
slightly greased.) rons dull pollinose, the upper part apparently 
brownish gray, the lower third silvery gray pollinose; pile of upper 
frons and vertex black, all the rest of the pile of the head white. 
Pile of mesonotum largely short, reclinate, and white, but 
there are a few short biack pile in the median portion. Abdomen 
black in ground color and almost wholly gray pollinose; on the 
second, third, and fourth segments a basal, dark-brown, semicircular 
mark, narrow on the sides and divided by a median grayish line; first 
four segments with short reclinate white pile, the rest of the abdo- 
men with short erect black pile. Wings gray hyaline, with cell M-3 
wide open in both wings of the type specimen. 
Type localities.—Peaceful Valley, Colorado, and Aweme, Manitoba, 
Canada. Holotype, a male, collected at Peaceful Valley, Colorado, 
August, 1919 (T. D. A. Cockerell), and allotype, a female, collected at 
Aweme, Manitoba, Canada, June 13, 1911 (E. Criddle). 
Types.—Holotype in the United States National Museum, Cat. 
No. 25937. Allotype in the Philadelphia Academy of Natural 
Sciences. 
There is a male paratype in the Academy of Natural Sciences in 
Philadelphia collection, taken with the allotype at Aweme, Manitoba. 
The species is closely related to candidata, cinerascens, and vialis. 
The male is easily recognized by the peculiar structure of the geni- 
talia. It is evidently a northern form and may have a rather wide 
distribution. 
