256 THE CANADIAN ENTOMOLOGIST 



3. At least the hind tibia partly or entirely yellowish testaceous; mid tibia 



without an anteroventral bristle; hind tibia with 2 posterodorsal 



bristles divisa Meigen. 



All tibiae black; mid tibia with an anteroventral bristle; hind tibia with 3 



or more postero ventral bristles 4. 



All tibiae black or fuscous; mid tibia with an anteroventral bristle; hind 



tibia with 2 posterodorsal bristles proximo. Malloch. 



4. Dorsum of thorax and abdomen slightly blue-gray pruinescent; longest 



hairs on arista much shorter than width of third antennal segment; mid 



tibia with one anterodorsal bristle arctica Malloch. 



Dorsum of thorax and abdomen densely pale gray pruinescent; longest 

 hairs on arista at least as long as width of third antennal segment mid 

 tibia with 2 anterodorsal bristles polita Malloch. 



5. Legs brown or dull yellowish, not deep black; basal dorsal abdominal 



segment largely yellowish testaceous on each side; hind tibia with 2 

 posterodorsal bristles; longest hairs on arista distinctly longer than 

 width of third antennal segment; small species, not over 5 mm. in 



length suhpellucens Malloch . 



Legs deep black; abdomen not yellowish at base; hind tibia with 3 or more 

 bristles on posterodorsal surface, the basal one sometimes very weak... 6. 



6. Hind femur with several long hair-like bristles at base on posteroventral 



surface :-7. 



Hind femur with one bristle at base on posteroventral surface IL 



7. Costal thorns both small, sometimes barely distinguishable from the 



adjacent setulae, never as long as the inner cross-vein; parafacial in 

 profile conspicuously narrowed below, not nearly as wide as third an- 

 tennal segment at lower margin of eye uniformis Malloch. 



. At least one of the costal thorns long and conspicuous, sometimes as long 

 as the inner cross-vein; parafacial in profile but little narrowed below, 

 as wide as third antennal segment for nearly its entire length 8. 



8. Hairs on arista not longer than its basal diameter; mid tibia with 2 antero- 



ventral bristles; spines on apical genital segment short and strong, 

 12-14 in number; hind tibia with one or more posterior 



setulae alaskensis, sp. n . 



Hairs on arista much longer than its basal diameter; mid tibia with 1 

 anteroventral bristle ' 9. 



9. Thorax with two or three pairs of weak acrostichals and some hairs m 



front of suture ; genital segment similar to that of 



alaskensis seticanda Malloch . 



Thorax with central area in front of suture with 4 or 6 series of weak 

 hairs 10. 



10. Apical genital segment with about a dozen short, strong spines; hind 



tibia with 4 posterodorsal bristles ..horealis Malloch. 



Apical genital segment with 2 fine, short bristles and some hairs; hind 

 tibia with two or three posterodorsal bristles flavohalterat-a Malloch. 



11. Mid tibia with one or more short bristles immediately basad of the antero- 



dorsal one; thorax with two or three pairs of presutural 



acrostichals elongata Malloch. 



