2I 6 NORTH AMERICAN DIPTERA. 



21. Two submarginal cells present 26 



Three submarginal cells. .22 



22. Bare species; tibiae without bristles; abdomen narrow. 



Amphicosmus. 

 More or less pilose species; tibiae with bristles. . . 23 



23. Antennae as long as the head, the third joint not longer than the 



first two together 24 



Antennae shorter than the head; the third joint twice as long as 

 the first two together. Exepacmus. 



24. First antennal joint not thickened. ..... 25 



First antennal joint extraordinarily thickened. . . Ploas. 



25. ' Scutellum deeply sulcate longitudinally'. . . Gemmaria. 

 Scutellum convex; not sulcate (13, 14). . . Lordotus. 



26. Anal cell open. 29 



Anal cell closed. . 27 



27. Proboscis short; frontal triangle of male large (fig. 82) . 



Oncodocera. 

 Proboscis elongate. . . , 28 



28. Third joint of the antennae with long bristly hairs; face with long 



hair Acreotrichus. 



Third joint of antennae withoiit, or with short bristly hairs above; 

 face bare or short pilose (15, 16) .... Phthiria. 



29. Body clothed with more scales than hairs, gibbous; antennae long, 



the first joint unusually long (2O, 21, p. 80). Lepidophora. 

 Body clothed chiefly with hair, or nearly bare. ... 30 



30. Alulae wholly wanting; thorax and posterior margins of the ab- 



dominal segments with bristles; all the tibiae with bristles; first 



and third antennal joints subequal. . Sphenoidoptera- 



Flies not having the above assemblage of characters. . . 31 



31. Body more or less pilose; tibiae usually bristly. ... 32 

 Body bare; tibiae bare or feebly bristly. .... 37 



32. Both basal cells of nearly equal length (17). Sparnopolius. 

 First basal cell distinctly longer than the second. . . 33 



33. Third antennal joint but little longer than the first; mesonotum 



of male sometimes muricate and the costa denticulate (19, p. 80) . 



Eclimus. 



