SNOW: AMERICAN PLATVPEZID^. 147 



the hind tarsal joints on inner side with short, thick golden pile. 

 Halteres with yellow stem and fuscous brown knob. Wings hyaline, 

 slightly infuscate near the tip, stigma yellowish; auxiliary vein ends 

 far beyond the anterior crossvein; posterior crossvein close to border 

 of wing, distant on fifth vein one-third to two-thirds its length; 

 second posterior cell long; posterior branch of fourth vein short. 



Female. A single female specimen caught at the same time with a 

 male shows slight differences in the coloration of the abdomen; first 

 segment covered with a lightish, somewhat yellowish pollen, and 

 shows but a mere trace of black along the incisure; second seg- 

 ment anteriorly with similar pollen and with a large black triangle 

 arising posteriorly and not reaching the anterior border of segment; 

 third, fourth and fifth segments with smaller similar triangles, else- 

 where with cinereous pollen, which covers nearly the whole of the 

 fifth segment, and quite the whole of following segments; sides of 

 first and second segments with soft, silky yellowish pile; sides of fol- 

 lowing segments with coarser short black pile. Legs yellow except a 

 preapical fuscous spot on hind femora and the blackish hind tarsi 

 (PL 12, fig. 3); the hind tarsi are much smaller and present the same 

 type of structure noticed in other females of the genus (see 

 plate); the joints on their inner side furnished with short, brush-like, 

 golden pile as in the male; the long light-colored femoral pile noticed 

 on the male is absent, as well as the tuft of black pile on the hind 

 femora in that sex. 



Length of male 4 to 6 mm.; of female 4 mm. 



Seventy-five males and one female, Hop Canyon, Magdalena Mts., 

 N. M., 8,000 feet. Nearly all were taken from August 19th to 21st. 

 These strange insects were found dodging and soaring in the air in 

 assemblages of, say, a dozen individuals each, all males. None were 

 caught outside an area of about an acre. They grouped themselves 

 in midair under the overhanging boughs of some large spruce, and 

 when an attack was made upon them with the collecting net they 

 would dodge and scatter, to resume their zig-zag flight a little higher 

 up. The collectors were often obliged to mount a stump or to splice 

 a branch to the net handles to give the nets higher sweep. In flight 

 these insects allow their hind feet to hang heavily downward and look 

 as if they were carrying some heavy burden. Only the merest acci- 

 dent brought the female to net. The writer was watching an inac- 

 cessible group of males in the air when an apparently large and black 

 object slowly passed within an inch or two of his eye. A lucky 

 stroke of the net and the thing was found to be no larger nor blacker 

 than a pair of small brown flies. This species was found only in the 

 warmer portions of the day. Three or four days after they were first 

 discovered they apparently disappeared. 



