462 NORTH AMERICAN DIPTERA 



454. Fifth vein bristled Polygastropsis Townsend 



Fifth vein bare 455 



455. Apical abdominal segment of the male very strongly produced pos- 



teriorly; ocellars small Urophillophila Townsend 



Apical abdominal segment not produced; ocellars absent. 



Opsoleskia Townsend 



456. Third antennal segment never with the apical corner acutely pro- 



duced 458 



Apex of the third antennal segment produced as a short, sharp spur 

 (5) 457 



457. Prosternum bare Acemya Desvoidy 



Prosternum haired (Myothyria Wulp) Ceracia Rondani 



458. Apical cell ending at or near the wing-tip 458 



Apical cell ending far before the wing-tip; cheeks usually twice as 



wide as third antennal segment; abdomen with discals; two pi'e- 

 sutural acrosticals and three dorsocentrals. 



*Dexodes Brauer & Bergenstamm 



459. Third antennal segment rarely unusually wide and long, if so the 



palpi yellow or the facial depression not unusually deep 460 



Third antennal segment more than six times as long as the second, 

 unusually wide; facial depression very deep; palpi white. 



ffidematocera Townsend 



460. Over 9 mm. in length; apical cell narrowly opened or closed in the 



costa; discal crossvein joining the fourth vein three- fourths the dis- 

 tance beyond the small crossvein; abdomen with discals. 



Pelatachina Meade 

 Usually less than 8 mm. in length; not possessing the above combina- 

 tion of characters 461 



461. Cheeks not over one-third as wide as the eye-height 462 



Cheeks two-thirds as wide as the eye-height Clista Meigen 



462. Second abdominal segment with dorsal bristles 463 



Second abdominal segment without dorsal bristles. Calpodomyia Townsend 



463. Bristles of the thorax suberect; first and fifth veins never bristled. . . .464 

 Bristles of the thorax subappressed; first and fifth veins often bris- 

 tled (148, 189) (cf.Spathidexia) fActia Desvoidy 



464. Ventral margin of at least the second tergite in the female with 



stout, spinose setulas; knob of halteres brown in male 465 



Tergites without such setulae in female; halteres yellow 466 



465. Second antennal segment of male large, half as wide as long. 



Elephantocera Townsend 

 Second antennal segment of male not large, three times as long as 

 wide Celatoria Coquillett 



466. Arista bare, short pubescent or extremely short plumose 468 



Arista very conspicuously short plumose; genital opening apical 467 



467. Three pairs of strong presutural acrosticals (151, 157). 



Thelairalia, n. g. 



* Cun-an, 1927, Can. Ent., lix, p. 23. 



t Ciuian, 1933, Amer. Mus. Kovit. No. 614. pp. 1-7. 



