18 PROCEEDINGS OF THE NATIONAL MUSEUM. voi. 65 



7. Apices of tibiae pale; superior forceps of male hypopygium long, but not 

 very slender, their inner margins on apical third minutely serrate, inferior 

 pair cleft at apices, the arms of dissimilar lengths; fifth steruite with 

 two slender chitinized processes on posterior margin which are directed 

 backward (figs. 10, 10a) ; no dark spot in middle of mesopleurum. 



serrata Mallodi. 

 Apices of tibiae blackened; superior forceps of male hypopygium not ser- 

 rated on inner margins apically ; usually a distinct brown spot in middle 

 of mesopleurum 8 



<5. Superior forceps of male hypopygium short and stout, inferior pair with 

 the apical branches of almost equal size; fifth sternite of male with two 

 slender backwardly directed processes on posterior margin (figs. 11, 12). 



obttisilamellata Malloch. 



Superior forceps of male hypopygium long and slender, branches of inferior 



pair unequal in size (figs. 15, 15o) ; fifth sternite of male without processes 



on posterior margin quadrilineata Loew. 



9. Superior forceps of male hypopygium long and slender, inferior pair lon.ir 

 and slender, much curved, with a short tooth beyond middle (fig. 13) ; 

 larger species, 4 mm. in length, color pale, the spots on abdomen sometimes 

 but little darker than remainder of segment; central pale stripe on 

 mesonotum distinctly narrowed at anterior extremity, annulata Melander. 

 Superior forceps of male hypopygium short and stout, their apical margins 

 concave (figs. 14, 14a) ; small species, 3 mm. in length; color darker, the 

 spots on abdomen always fuscous and much darker than remainder uf 

 segment ; central pale stripe on mesonotum not distinctly narrowed at 

 anterior extremity pictiventris Malloch. 



10. Thorax with two pairs of dorsocentrals ; shining yellow species with a 



round shining black spot on each side of the apical two or three abdomi- 

 nal tergites rotundicornis Loew. 



Thorax with three pairs of dorsocentrals, abdomen not as above 11 



11. Yellow species ; frons glossy, with a black spot in middle ; apical half of 



third antennal segment black (Wyoming, Montana) cyclops Melandor. 



Yellow species; frons shining unicolorous yellow; third antennal segnu'ut 



slightly infuscated above on apical half monticola Melaiider. 



Black species frons largely, antennae entirely, blackish 12 



12. Face with a round black or brown spot on each side in center; densely pale 



gray pruinescent species ; thorax vittate ; tibia with a pale band at base 



and another beyond middle vittigera Coquillott. 



Face immaculate ; moderately pruinose species, with the thorax not vittate 

 and tibia not banded lo 



13. Face and frons highly polished, only the facial orbits gray pruinescent ; face 



slightly bulbous in center just below antennae; third antennal segment at 

 least three times as long as wide; arista short haired; acrostichals in 



four irregular series elisae Meigen. 



At least the face gray pruinescent, not bulbous ; third antennal segment 

 about twice as long as wide 14 



14. Frons opaque, indistinctly reddish on anterior margin ; thorax opaque, with 



rather dense brownish pruinescence, the acrostichals in two series; arista 



nearly bare brachysoma Coquillett. 



Frons shining, especially on orbits, conspicously reddish testaceous on 

 anterior margin; thorax shining, faintly gray pruinescent, the acrostichals 

 in four series between anterior dorsocentrals : arista pubescent, 



hyalinata Meigen (=nigrans Melander). 



