NO. 2141. DIPTERAFROM ANTS NESTS— COCKERELL AND ANDREWS. 55 



Ilahitat. — Boulder, Colorado. Two of the soft, slug-like larvae were 

 found in a nest of Formioa fusca argentea Wheeler, April 13, 1915, at 

 the foot of Flagstaff Hill, Boulder. They were placed in a glass jar 

 with soil and some of the ants, and a third larva, found later, was 

 added. On April 15, one of the larvae became a pupa. On May 14, 

 two male flies hatched, and two days later a female appeared. On 

 June 8 a female was caught at Pulpit Kock, Boulder. The type is a 

 male. This is a large robust species, the sexes with quite differently 

 colored hair, but both having the front broad. It is much larger than 

 M. tristis, and differently colored. The size suggests 3f. megalogasfer 

 {homhiformis) , but the color is different, and the front of the male 

 is not narrowed in the middle, while the second antennal- joint is much 

 more than a third the length of third. It is larger than M. xanthopl- 

 lis Townsend, from California, and quite differently colored; in 

 seanthopilis the hair is entirely brassy yellow (more orange in the 

 male) , without black. 



MICRODON TRISTIS, subspecies. 



Female. — Eobust; length (not including antennae), 12 mm.; width 

 of abdomen, G mm. ; length of wing, 9 mm. ; general color, black, 

 with shining pale hair; antennae, black; front broad, but narrower 

 than face ; scutellum with a pair of small tubercles, hidden by hair ; 

 penultimate segment of abdomen at sides nearly or quite as long as 

 the two preceding together. Head black, clothed with glittering very 

 pale yellowish pile; eyes bare; transverse groove of front shallow, 

 above it the integument is purplish black, while behind the eyes it is 

 very faintly greenish ; antennae elongate, first joint longer than third, 

 second more than a third length of third, but not nearly half; thorax 

 purplish-black, with rosy or coppery tints on disk, thinly clothed with 

 hair like that of head ; abdomen black, with extremely faint greenish 

 tints; glistening pale hair on lateral margins of segments, covering 

 dorsal surface of first segment, hind margin of second (broadened in 

 middle), and forming a very broad band, widely interrupted in mid- 

 dle, along posterior marginal area of third, apical part of abdomen 

 with scattered pale hair ; the apparently bare parts of abdomen have 

 thin black hair; legs black, with pale hair, orange on inner side of 

 tarsi; hind tarsi thickened; wings dilute cinereous, pale reddish 

 basally and in costal region, outer veins bordered by dusky clouds; 

 outer corners of first posterior and discal cells broadly rounded, that 

 of first posterior minutely appendiculate, but discal not; angle 

 formed on outer side by first posterior and discal cells a little greater 

 than a right angle ; stump in first posterior cell before middle. 



Male. — Superficially exactly like female, with the same colors, ex- 

 cept that first abdominal segment is more distinctly green; front 

 strongly narrowed above, the transverse groove, at the narrowest 



