154 NORTH AMERICAN DIPTERA 



20. Dorsal process of third antennal segment unusually long, extending to 



third annulus 21 



Dorsal process moderately long or forming a tooth, sharp edge, or 

 weak angle 22 



21. Fore tibiae strongly swollen; hind tibias ciliate with long hairs (23, 30). 



Stibasoma Schiner 

 Fore tibije not or hardly swollen; hind tibiae not ciliate (14, 24), 



Dichelacera Macquart 



22. Subcallus strongly swollen; first antennal segment much enlarged.... 23 

 Subcallus normal; first antennal segment not or slightly enlarged 



(11, 12, 27, 32) Tabanus Linnsus 



23. First antennal segment subglobular as well from above as from the 



sides; all tibiae strongly swollen Bolbodimyia Bigot 



First antennal segment much produced downward (in side view), but 

 not widened seen from above; tibiae not or hardly swollen (13). 



Snowiellus Hine 



