GG NORTH AMERICAN DIPTERA. 



The contact of tlic discal cell witii the tliird posterior at least twice as 

 long as its contact with the fourth posterior, the latter contact often 

 merely punctiforni. ..... Anthrax Scopoli. 



13. Wings with three posterior cells. 39 



Wings with four posterior cells. ....... 14 



14. First posterior cell closed 15 



First posterior cell open. ........ 22 



15. Three subinarginal cells present. ...... 10 



Two subniarginal cells. ........ 17 



10. Head broader than the thorax; i)Osterior orbits not excised. 



Pantakbes Osten Sacken. 

 Head narrower than the thora.x ; posterior orbits excised. 



Tkiplasius Loew. 



17. First basal cell longer tiian the second 18 



First basal cell not longer than the second. .... 21 



18. Proboscis very short, not protruding beyond the oral margin ; anal cell 



usually closed; large species (Cen. America). Anisotamia Macquart. 

 Proboscis more or less elongate; anal cell ojien. ... 19 



19. First posterior cell closed at some distance from the border of the 



wing 20 



First posterior cell narrowed, or closed in or near the margin of the 

 the wing; small species (5-0 mm.) . Tiilipsooaster Rondani. 



20. Head comparatively small ; the cmargination of the occipal orbits al- 



most imperceptible Bombylhs Linne. 



Head broad ; cmargination of the occijjital orbits distinct. 



Heterostylum Macquart. 



21. Face thickly clotlied with pile. . Anastoschus Osten Sacken. 

 Face sparsely clothed with pile. . . . SvsrtEciiLrs Loew. 



22. Two submarginal cells present. ....... 27 



Three submarginal cells present. ...... 23 



23. Bare species; tibiaj without bristles. . Ampiiicosmus C()<iuillett. 

 More or less pilose species; tibia; with bristles. .... 24 



24. Antenna; as long as the head, the third joint not longer than the first 



two together. .......... 25 



Antennse shorter than the head, the third joint twice as long as the first 

 two together . Exepacmus Coquillett. 



25. First antennal joint not thickened. ...... 20 



First antennal joint extraordinarily thickened. . Ploas Latreille. 



20. "Scutellum deeply sulcate longitudinally". Geminaria Coquillett. 

 Scutelliim convex, not sulcate Loudotcs Loew. 



