MALE. Eyes bare. Face greenish yellow on the sides, yellow in the middle; a rather broad black line marks the border of the mouth and is lost in the black of the cheeks. Frontal triangle yellow, with long black pile. Antennae dark brown, more or less reddish below. Pile of occiput light yellow. Dorsum of thorax deep metallic green, the scutellum olivaceous yellow; both with light yellow pile. First segment of the abdomen shining black; second segment opaque black, with the lateral margins and hind border shining, and with a broad, yellow, interrupted band, not reaching the lateral margins; third segment similar, but with the yellow band somewhat wider, interrupted or subinterrupted and slightly bilaterally oblique; fourth and fifth segments orange-red, the sides narrowly black; the fourth segment shows indistinctly a broad interrupted band of a somewhat lighter color, corresponding to the yellow bands of the preceding segments. Legs light brown; basal third of the front and middle femora and basal half of the hind femora black. Wings hyaline, stigma yellowish. FEMALE. Head wanting. Thorax purplish brown. The yellow band on the second abdominal segment narrower, the second band straight, narrower and interrupted. Legs light brown, except the proximal end of the femora, which is black. Length 9 millimeters. Three males and one female, Colorado. =Syrphus pauxillus= Williston. Two specimens from Colorado undoubtedly come here. The species was described from a single male specimen. A female specimen offers the following differences or additions: Length nine millimeters, mesonotum more greenish black or bronze, the pile obscure whitish; fifth abdominal segment without yellow spots on the anterior angles; legs yellow, with the basal half of the front and middle femora, the hind femora except the tip, a broad band on the hind tibiae, and the hind tarsi, black. =Syrphus ribesii= Linne. Five specimens, Colorado. =Syrphus americanus= Wiedemann. Numerous specimens, Colorado. =Syrphus umbellatarum= Schiner. Five female specimens, Colorado. The only western locality heretofore given is Arizona (Williston). =Allograpta obliqua= Say. Five specimens, Colorado. =Mesogramma marginatum= Say. Numerous specimens from Colorado, showing very great variation. =Sphaerophoria cylindrica= Say. Twenty specimens, Colorado. I think the specimens belong here, though a positive identification is hardly possible at present. =Rhingia nasica= Say. One specimen, Colorado. This is the first time that this species has been recorded from beyond the Mississippi. =Copestylum marginatum= Say. Two specimens, Colorado, representing the extremes of variation in the species. The male corresponds to _C. lentum_ Williston. Specimens of this species were bred from _Opuntia missouriensis_, in company with others of _Volucella fasciata_ Macq. =Sericomyia militaris= Walker.