2I 6 NORTH AMERICAN DIPTRRA. 



21. Two submarginal cells present. ...... 26 



Three submarginal cells. . . . . . . . 22 



22. Hare 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 antenna! joint not thickened. ..... 25 



First antenna! joint extraordinarily thickened. . . Ploas. 



25. 'Scntellum deeply snlcate longitudinally'. . . Geminaria. 

 Scutellum convex; not snlcate (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 without, or with short bristly hairs above; 

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



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



the first joint unusually long (20, 21, p. 80 1. 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 tibia.' with bristles; first 



and third antenna! joints subequal. . Sphenoidoptera- 



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



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

 Body bare; tibise 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 antenna! joint but little longer than the first; mesonotum 



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



Eclimus. 



