THE CANADIAN ENTOMOLOGIST 255 



11. Parafacial in profile at base of antenna? distinctly broader than third 



antennal segment; eyes separated by at least as great a distance as 

 width across posterior ocelli; processes of fifth sternite broad, fringed 

 along their inner margins with fine hairs, the disc with a few bristly 



hairs 12. 



Parafacial in profile at no point as broad as third antennal segment; eyes 



separated by about width of anterior ocellus; processes of fifth sternite 



narrow, fringed along their inner margins with hairs which apically 



become longer and are incurved, the disc wath long, bristly hairs which 



are similar to those on inner margins uniformis Malloch. 



12. Thorax with at least one pair of well-developed presutural acrostichals; 



mesopleura with 3 or 4 bristles near upper anterior 



angle coloradensis Malloch. 



Thorax without distinguishable presutural acrostichals, with fine hairs 



only; mesopleura with a few bristly hairs near anterior upper angle .12a. 

 12a. Longest hairs on arista much longer than its basal diameter; hind tibia 



with three posterodorsal bristles flavoh altera ta Malloch. 



Longest hairs on arista not as long as its basal diameter; hind tibia with 



three long and one or two short posterodorsal bristles con grna Malloch. 



13. Fourth (visible) tergite at middle much shorter than third; hind femur 



without bristles on posteroventral surface except one at apex and a 



small one near base; arista plumose basally dongata Malloch. 



Fourth tergite at least as long as third; hind femur with some bristles on 

 basal half .of posteroventral surface 14. 



14. Third tergite with very short bristles in lateral tuft, the tuft not con- 



spicuous, the tergite not much narrowed laterally; longest hairs on arista 



longer than its basal diameter borealis Malloch. 



Third tergite with a conspicuous tuft of long bristles at lateral margin, 

 the tergite much narrowed laterally 15. 



15. Longest hairs on arista about as long as width of third antennal segment; 



tergal tuft very dense, the bristles rather uniform in length, not extend- 

 ing beyond apex of fourth tergite ambigua Meigen. 



Longest hairs on arista not longer than its basal diameter; tergal tuft not 

 \ery dense, the bristles of unequal lengths, some of them extending to 

 apex of abdomen alaskensis, sp. n. 



FEMALES. 



1. Hypopleura with a few long hairs on upper margin in front of spiracle, 



rarely these hairs absent or almost so, but all species have the orbits 

 with a number of setulose hairs, which are sometimes very long, laterad 

 of the supraorbital bristles; apical genital segment without short-curved 



spines , 2 



Hypopleura bare; no setulose hairs laterad of the supraorbitals; apical 

 genital segment with a few short-curved spines or bristles besides the 

 usual hairs 5. 



2. Halteres black; mid femur with a few strong bristles and numerous long 



setulose hairs on anteroventral surface; parafacial in profile distinctly 



broader than third antennal segment nigerrima Malloch. 



Halteres with vellow- knobs r. 3 



