6 NORTH AMERICAN DIRTERA. 



41. Between the third and fourtli longitudinal veins and sub-parallel witli 



them, crossing the anterior cross- vein, a spurious longitudinal vein, 

 or, when rarely not present, the first posterior cell closed a consid- 

 erable distance from the border. .... Syrpiud^i;. o^ 

 Spurious vein never present; first posterior cell not closed before the 

 margin; eyes very large; small species. . . Pipunculid.e.v ^ 



42. Proboscis horny and elongate, often folding back near the middle; ab- 



domen never with bristles ; tibiae without terminal sx>urs or if with 

 spurs, the face with a median ridge, and the proboscis folding; first 

 posterior cell closed or narrowed. .... Conopid/e. ^ I 

 Proboscis fleshy and not elongate ; if elongate and slender, with or with- 

 out a median hinge, the body with distinct bristles, or the bristle 

 of the antennae plumose. .... MusciDiE sens. hit. 76 



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



upon the dorsum of the thorax ; first' joint of tarsi not abbreviated. 



NYCTERIBIDyTJ. ' 



Winged or wingless flies, parasitic upon birds or mammals; head flat- 

 tened, sunk into a shallow emargination of the thorax; first joint of 

 the four anterior or of all the tarsi abbreviated. . Hippoboscid.e. /^i- 



