The True Flies 



Calypteres small or rudimentary, at least one pair of tibiae 

 provided with distinct spurs at the apex of the inner 

 side Family Leptidce. 



17 Third joint of the antennae distinctly annulated 18 



Third joint not annulated 20 



18 Discal cell lying in the middle of the width of the wing, pos- 

 terior margin of the wing encompassed by a vein 19 



Discal cell lying between the middle of the width of the wing 

 and the costa, posterior margin of the wing not encom- 

 passed by a vein Family Stratiomyiidce. 



19 Tibiae never furnished with terminal spurs, calypteres rudi- 

 mentary; large flies from Middle and South America. . . 

 Family Acanthomeridce. 



Tibiae provided with terminal spurs on at least one pair, 

 calypteres very large; horse-flies. . . . Family Tabanidce. 



20 Head small, much narrower than the very convex thorax, 



calypteres very large; hump-backed flies 



Family Acroceridce. 



Head at least as wide as the depressed thorax, calypteres very 

 small ; flies not at all hump-backed. Family Nemestrinidce. 



21 When five posterior cells are present the fourth vein ends 

 before the extreme apex of the wing; when less than 

 five the anal cell is much longer than the second basal 

 and the third vein ends below the tip of the wing, dis- 

 cal cell always present (Super-family Bombylioidea.)..22 



When five posterior cells are present the fourth vein ends 

 below the extreme apex of the wing, when less than 

 five the anal cell is wanting, or, if present, is shorter or 

 scarcely longer than the second basal, or the third vein 

 ends before the extreme apex of the wing, discal cell 

 sometimes coalescing with one of the other cells 24 



Super-family BOMBYLIOIDEA Coq. 



22 Wings provided with less than five posterior cells 23 



Wings provided with five posterior cells, fourth vein ending 

 before the wing tip, antennal style much narrower than 



the third antennal joint; inhabit the southwest 



Family Apioceridce. 



23 Style of the antennae flat, much wider than the third antennal 

 joint ; large, elongate, nearly bare flies . . Family Mydaidce. 

 87 " 



