156 



NORTH AMERICAN DIPTERA 



KEY TO GENERA 



Pantophthalmus species. 



1. Abdomen not or scarcely more than twice as long as wide, short and 



broad 2 



Abdomen three times as long as wide, long and narrow; Mydas-like 

 species Atopomyia Austen 



2, Third palpal segment almost always cylindrical, even when somewhat 



swollen and more or less pointed below, usually obtuse apically; facial 

 beak, if present and fairly long, strongly tapering and the ventral 

 spur on the posterior femora greatly reduced or almost absent. 



Pantophthalmus Thunberg 

 Third palpal segment broadened and laterally compressed, especially in 

 the female, pointed below; face with a long, narrow beak and the 

 posterior femora with a strong ventral spur. 



Rhaphiorhynchus Wiedemann 



