4 NORTH AMERICAN DIPTERA. 



19. Empodia developed pulvilliform, that is three nearly equal membranous 



appendages on the under side of the claws ..... 20 



Empodia wanting, rudimentary or linear, never developed like the 



pulvilli ..... ....... 22 



20. Tegula; very large; thorax and abdomen inflated; head small, eyes 



large; neuration varied ....... ACROCEUID.E. 



Tegulae of moderate size or rudimentary ...... 21 



21. Middle tibiae at least with spurs; no bristles on femora or tibia; ; third 



longitudinal vein furcate ; five posterior cells present (four in 



Dialysis); anterior cross- vein always distinct; third joint of the an- 



tennae with a bristle or slender style, usually terminal. LEPTID^E. 



Not such flies ........... 22 



22. Third longitudinal vein of the wings not furcate. ... 31 

 Third longitudinal vein furcate, two or more submarginal cells 



present ............ 23 



23. Arista or style of antenna? when present always terminal. . . 24 

 Arista dorsal, always present ........ 30 



24. Vertex and front distinctly hollowed out between the eyes; eyes of 



male never contiguous; basal cells large; mostly large flies. . 25 

 Front and vertex plane or convex. . .... 26 



25. Proboscis with fleshy labella at the tip ; neuration complicated, the 



fourth vein at least curves forward to terminate before the tip of the 



wing; palpi rudimentary or wanting ..... MYDAID^E. 



Proboscis without fleshy labella at tip, the under part forming a horny 



sheath; five posterior cells always present; palpi usually prominent. 



26. Five posterior cells in the wing; basal cells large. ... 29 

 Never more than four posterior cells in the wing. ... 27 



27. Third antennal joint without bristle or style ; three posterior cells; first 



posterior cell narrowed or closed, the fourth longitudinal vein termi- 



nating at or before the tip of the wing. . , . SCENOPINID.E. 



Third antennal joint usually with terminal style; four or three poste- 



rior cells; the fourth vein terminates beyond the tip of the wing. 28 



28. Anal cell narrowly open, or closed near the margin; discal cell pres- 



ent. ...... ... BOMBYLIID^:. 



Anal cell closed remote from the border, sometimes wanting; if closed 

 near the border (Hilarimorpha), the discal cell wanting. EMPID.E. 



29. Neuration intricate, the anterior cross-vein wanting or rudimentary, 



owing to the coalescence of the third and fourth veins for a longer 

 or shorter distance ; tibias without terminal spurs ; empodia and pul- 

 villi membranous, but frequently minute. . . NEMISTKINID^E. 



