104 PROCEEDINGS OF THE NATIONAL MUSEUM. you. 62. 
joints of antennae, base of third, face. and most of occiput gray 
pollinose; upper corner of frontal triangle velvety black. 
Thorax, scutellum, and coxae dull black, thinly gray pollinose and 
black pilose; black pile of anterior part of thorax and the scutellum 
dense and erect. Halteres blackish, the knobs gray pollinose. * 
Abdomen black, gray pollinose and silvery white pilose; pile on 
first segment erect white, silvery on the posterior margin, the rest 
of the pile on the dorsum reclinate and dense. Hypandrium black 
and densely pilose, some of the hairs black; the structure of the 
genitalia close to vialis Osten Sacken. Venter very sparsely pilose. 
Legs with black bristles. Femora black, black pilose; most of tibiae 
and base of tarsi yellowish, the tip of tibiae and most of tarsi black. 
Wings whitish hyaline, veins brown, stigma narrow and brown, cell 
M-3 closed and short petiolate. 
Female.—Length 9 mm. Quite different in general appearance 
from the male. Antennae about the same in structure, the pile at 
the base of the first jot white. Bristles of antennae and occiput 
black. Upper frons with short black pile, a few black hairs on the 
lower frons; lower frons and face silvery white pollinose, the former 
largely white pilose, the latter entirely so; upper frons grayish brown 
pollinose; between the two colors of the frons a velvet black line, 
wider at the sides. Occiput, cheeks, and palpi white pilose. 
Thorax black in ground color, obscured by dense gray pollen on 
the dorsum, pleura, coxae, and scutellum; two vittae and the lateral 
margins paler; pile of mesonotum very sparse, reclinate, and white; 
pile of the pleura and coxae white. Halteres as in the male. 
Abdomen black, but only the eighth segment shining, other seg- 
ments with a dense covering of gray and brown pollen; base of third 
and fourth segments semishining brown and spots on the anterior 
corners of fifth and sixth segments. Pile on the basal segments 
black, a few erect black hairs on the dorsum of the third and fourth, 
most of the fifth segment black pilose, and all of the sixth, seventh, 
and eighth. Legs colored as in the male, with reclinate silvery white 
pile on the femora and a few erect white hairs. Wing membrane 
white or whitish hyaline; cell M—3 closed in the margin of the wing. 
Ty pe locality.—Pacific Grove, California, on the upper beach, May 8, 
1906 (Dr. J. M. Aldrich). 
Types.—Male, Cat. No. 25938, U.S.N.M.; allotype, female, in 
same. 
There is a male paratype, taken at the same time with the 
types, in the National Museum collection. The species is easily 
distinguished in the male by the densely black pilose head and 
thorax, contrasting with the silvery white abdomen. ‘The wings 
are noticeably whitish, especially in the female. It is undoubtedly a 
sand-dune species of local distribution, like the following new species. 
