Eleven specimens, Colorado, which answer well to the descriptions. The metallic band of the fourth abdominal segment is sometimes interrupted, and there is usually a triangular opaque black spot near the anterior border of the fifth segment. “The female, hitherto unknown, has the front broad above, pollinose, except on the upper part, and with black pile; the thorax more shining metallic blue; the tibiae yellow, and on the third and fourth abdominal segments there is a narrow shining stripe, bisecting the black, as in the fourth segment of the male. The male has some long black hairs on the outer side of the front and middle tibiae, which are inconspicuous in the female. It is evident, from the lighter color of the tibiae, that Say’s specimens were females.” Williston, l. c. =Melanostoma mellinum= Linne. A single female specimen from Manitou Park. =Melanostoma, n. sp.=? MALE. Face and front dark metallic blue, shining, thinly covered with light-colored pollen; tubercle and epistoma black, shining, the former small. Antennae black, third joint yellowish red below, oblong. Pile of frontal and vertical triangles dusky. Thorax bronze-black, shining, sometimes bluish black, the pubescence white. Halteres yellowish. Abdomen long and narrow, with almost parallel sides; first segment metallic blue, shining; second segment opaque, or subopaque, black, with a light metallescent scallop on the sides, reaching to the distal third of the segment; third and fourth segments similar, marked anteriorly by a wide, interrupted, or subinterrupted blue fascia, deeply and widely emarginated, or concave behind; hind border of the third, and sometimes of the second segment, narrowly brown; fifth segment and the hypopygium metallic bluish green; sides of the abdomen with silvery white pile, longest and thickest at the base; the blue marking are whitish pruinose. Femora, except the tip, a broad ring on the tibiae, and the four posterior tarsi, black; elsewhere brownish or yellowish. Wings hyaline, stigma yellowish. Length 7-8 millimeters. =Eupeodes volucris=, Osten Sacken. Numerous specimens, Colorado. =Syrphus arcuatus= Fallen. Four specimens, Colorado. These specimens vary not a little from each other, and somewhat from the descriptions. One female is very small, not over seven millimeters in length, and with the spots on the third and fourth abdominal segments hardly oblique. One male has the hind femora black as far as the tip, while in three females the black does not extend beyond the middle. =Syrphus disjectus= Williston. A single female specimen, from Colorado, agrees well with the description drawn from males. The pile of the thorax is more whitish than orange-yellow, and there are light colored lateral margins on the anterior part of the thorax. =Syrphus ruficauda, n. sp.=, Plate vii, f. 3.