52 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62. 
quite distinct from western specimens; this eastern form has been 
given a new name, flavipennis. The color of the halteres is one of 
the characters differentiating the two forms; in the western form 
they are bright lemon yellow, in the eastern species pale brown. 
The cotypes in the National Museum are all of the western form, 
which has been designated as the true aldricht. There seems to be a 
slight difference in the California and Northwestern specimens, and 
it is quite possible that Coquillett’s original series will have to be 
split again when more specimens are studied from both localities. 
The following notes are made from specimens taken in Oregon, 
Washington, Idaho, Montana, western Canada, and California: 
Male.—A few minute black hairs on the frons above the antennae; 
cheeks dull black. In most specimens the thorax is very faintly 
pollinose, almost shining black; pile reclinate yellow and erect whit- 
ish or yellowish white, the two vittae very faintly perceptible, if at 
all. Base of the scutellum shining, the apical half whitish pollinose. 
Lateral margins of the abdominal segments beyond the first broadly 
shining black; second and third segments with white posterior bor- 
ders; fifth, sixth, and seventh segments very short, the seventh 
searcely visible. Genitalia reddish, with reddish yellow pile. The 
tibiae are reddish yellow with black apices. 
Female.—Unusally 1 to 2 mm. longer than the male. Ocellar 
tubercle and usually a short strip on each side gray pollinose, but 
most of the frons shining black (fig. 42), much as in P. frontalis 
Lower occiput shming black except a white rim next to the eye. 
Thoracic vittae very distinct; pile of the thorax and scutellum yellow- 
ish, very short and sparse; pile before the halteres shorter than in 
the male. First abdominal segment with some gray pollen, the other 
segments shining black, with erect black pile beyond the third seg- 
ment. Wings darker than in the male, with a yellowish gray tinge. 
Type localities —New Jersey, Montana, Wyoming, and California. 
Cotypes.—Male and female, Cat. No. 10414, U.S.N.M.; others in 
C. W. Johnson’s collection. 
Distribution.—The following localities are given from a study of 
26 males and 18 females. 
Canada: Aweme, Manitoba, July 11 (Criddle), [A. N. S. P.]; 
Vancouver Island (H. Edwards), [Amer. Mus.]. 
Wyoming: Torrey’s Lakes, September 7 [Amer. Mus.]; Niobrara 
County, August 22 (EK. G. Holt), [Biol. Surv.]. 
Colorado: Denver, August (E. S. Tucker), Coq. det. [Kans. U.]. 
Montana: Gallatin County, July 18, elevation 5,500 feet, and 
August J5, elevation 6,000 feet; Missoula, August 17; Musselshell, 
August 17 [all Mont. Exp. Sta.]. 
Idaho: Boise, June 13 (Fisher), [Biol. Surv.]; Malad, June 20 
(Cole), [Cole]; Lewiston (C. V. Piper), [R. C. Shannon]. 
