■jo NORTH AMERICAN DIPTKRA. 



wing; pal])i small or wanting. Large to very large, bristleless 



flies Mydaidae, 190 



Proboscis without fleshy labella at tip, horny and rigid; five pos- 

 terior cells almost always present; palpi usually prominent. 

 Mostly large, bristly, predaceous flies. Asilidae, 192 



26. Five posterior cells in the wing; basal cells large. . . 27 

 Not more than four posterior cells.* ..... 29 



27. Venation intricate; empodia and pulvilli membranous, but fre- 



quently minute (see 21).. 

 Venation not intricate, the anterior cross-vein always apparent. 28 



28. The fourth vein terminates before tip of wing; male sexual organs 



prominent; males dichoptic. . . . Apioceridae , 188 

 The fourth vein terminates beyond the tip of the wing; male sex- 

 ual organs small; males often holoptic. . Therevidae, 205 



29. Third antennal joint without bristle or style; three posterior cells, 



the first narrowed or closed; the fourth vein terminating at or 



before the tip of the wing. . . . Scenopinidae, 208 



Third antennal joint usually with a terminal style; four or three 



posterior cells; the fourth vein terminates beyond tip of wing. 30 



30. Anal cell narrowly open or closed near border of wing (if discal 



cell wanting, see Hilar imorp ha p. 157, footnote). 



Bombyliidae, 210 



Anal cell closed remote from border, sometimes absent; discal cell 



not rarely absent Empididae, 218 



31. Wings pointed; no cross-veins, save at base; second basal cell 



short; arista terminal; small flies. . Lonchopteridae, 240 

 Wings not lanceolate 32 



32. Anal cell elongate, acute, closed toward or near the lxmler of the 



wing; second basal cell usually long. .... 36 



Anal cell, if present, short, closed remote from the border of the 

 wing, not acutely produced (rarely produced in a narrow, lobe- 

 like prolongation.) ........ 33 



H- Second basal cell confluent witli discal cell, or the discal cell ab- 

 sent; auxiliary vein usually vestigial or indistinct; anal cell 



often absent; usually small flies 34 



Second basal cell separated by a cross-vein from a complete discal 

 cell; auxiliary vein and anal cell usually complete. . 40 



* Five in a very few species of Bombyliidae, 



