202 ENTOMOLOGICAL NEWS [xxxii, '21 







8. Large species, 4.5 to 5 mm. in length ; arista with distinct but short 

 hairs ; thorax opaque gray, not vittate ; base of abdomen narrowly 

 yellow, the dorsum with three pairs of black spots comprcssa Stein 



- Smaller species, averaging 2.5 mm. in length ; arista almost bare, the 



pubescence visible only under a high-power lens ; abdomen either 

 broadly yellow at base or entirely blackish gray ') 



9. Dorsum of thorax opaque gray, with three poorly denned brown lines, 



one in center and the others along the line of dorsocentrals ; base 

 of abdomen broadly yellow, the dorsum with four pairs of black 

 spots : mid and hind femora each with a short posteroventral bris- 

 tle ; longest bristle on hind tibia not one-fourth as long as tibia, 



frisoni Malloch 



- Dorsum of thorax distinctly shining, blackish ; base of abdomen not 



yellow, dorsum with three pairs of black spots ; mid and hind fem- 

 ora each with a very long median posteroventral bristle ; longest 

 bristle on hind tibia about one-third as long as, tibia, 



oi'cgoncnsis Malloch 



- Dorsum of thorax opaque gray, not vittate; abdomen not yellow at 



base, with two pairs of distinct dorsal spots, one on the third and 

 the other on the fourth tergite ; mid and hind femora each with a 

 very fine median posteroventral bristle, the one on hind femur very 

 long ; hind tibia with the bristles very slender, the anterodorsal one 

 over half as long as the tibia argenticeps Malloch 



10. Antennae entirely black; mid tibia with an anterodorsal and a post- 

 erodorsal bristle 11 



- Antennae partly reddish or yellowish ; mid tibia with only the post- 



erodorsal bristle 14 



11. Scutellum with the apical pair of marginal bristles absent or minute, 

 the basal pair very long and strong ; abdomen yellowish brown, 

 without paired dorsal spots dichacta Malloch 



- Scutellum with two pairs of strong marginal bristles 12 



12. Large species, averaging 5 mm. in length or over; pruinescence of 

 body brownish yellow ; tarsi not longer than tibiae ; hind femur with 

 some very strong bristles on basal half of posteroventral surface; 

 abdomen without dorsal spots or with a very poorly defined pair on 

 fourth tergite fhnnfrons Stein 



- Smaller species, not exceeding 3 mm. in length ; pruinescence of 

 body either whitish or bluish gray ; hind femur without strong 

 bristles on posteroventral surface ; abdomen with the dorsal spots 

 fused, so that the surface presents the appearance of having a 

 broad brownish-black dorsal vitta, or a narrowly divided pair of 

 vittae 13 



13. Thorax and abdomen with whitish pruinescence; hind femur with 



very long anteroventral bristles; hind tibia with the anterodorsal 

 and preapical dorsal bristles over half as long as tibia, 



sctigcra Malloch 



