North American Diptera. 15 



45. First posterior cell widely open, not narrowed in the margin. 



Anthyomyid.e 



First posterior cell closed, or more or less narrowed. . 46 

 40. Antennal arista wholly bare Tachinid.*: 



Antennal arista distinctly pubescent or plumose. 47 



47. Arista bare on the distal part ; dorsum of abdomen rarely bris- 



tly before the distal part .... Sarcophagid.e 

 Arista plumose or pubescent to the tip 48 



48. Dorsum of abdomen bristly ; legs usually elongate. Dexid.e 

 Abdominal segments without bristles, except sometimes some- 

 what near the tip. Mcscid.e 



49. Wingless flies, parasitic upon bats; head not flattened, folding 



back upon the dorsum of the thorax ; first joint of tarsi not 



abbreviated. Nycteribid.e 



Winged or wingless flies, parasitic upon birds or quadrupeds ; 

 head flattened, sunk into a shallow emargination of the 

 thorax ; first joint of the four anterior, or all, tarsi abbre- 

 viated. HiPPOBOSCiD^: 



