AMERICAN DIPTERA. 151 



TABLE OF SUBFAMILIES. 



Palpi with one segment; antennae with a slender terminal style 2. 



Palpi with two segments; antennae with or without a thickened ter- 

 minal style, very rarely with a terminal arista 3. 



Marginal cell of wing open; very slender species leptogastrin.«. 



Marginal cell of wing closed, less slender or robust species asilin.-e. 



Marginal cell of wing open or rarely closed at extreme tip. 



DASYPOGONIN^E. 



Marginal cell of wing closed laphrin.*:. 



LEPTOGASTRIN^E and DASYPOGONIN.dE. 



TABLE OF GENERA. 



1. Fore tibias with a terminal claw-like spur (PI. II, fig. 3) 32. 



Fore tibiae without a terminal claw-like spur 2. 



2. Four posterior cells present, front very broad above; very small 



species Townsendia. 



Five posterior cells present (PI. II, fig. 1) 3. 



3. Pulvilli vestigial or wanting 4. 



Pulvilli normal 5. 



4. Third segment of antennae with an arista or aristiform style; ab- 



domen unusually long and slender (PI. VI, fig. 1). 



Leptogaster. 



Third segment of antennae with a short thickened style; abdomen 



not unusually long or slender (PI. XII, fig. 4)....Ablautns. 



5. Head narrow, about as high as broad (PI. V, fig. 3) ; face narrow 



above, broader and swollen below, in large part covered 



with hair; medium to large elongate species 6. 



Head very obviously broader than high (PI. V, fig. 1) 7. 



6. Antennae with a terminal style (PI. Ill, figs. 2, 3 and 4). 



Steiiopogon. 



Antennae without a style*; third segment long; fourth posterior 



cell closed before the border of the wing; black species, 



with or without red or yellow on the abdomen (PI. VII, 



fig. 5; PI. Ill, fig. 7) Ospriocerus. 



7. Fourth posterior cell closed before the borders of the wing (PI. 



II, fig. 1) 8. 



Fourth posterior cell open, rarely nearly closed (PI. X, fig. 5).... 15. 



8. Antennae much elongate, apparently of five segments (PI. IV, figs. 



2 and 3) 16. 



Antennae not elongate, composed of three segments, without a 

 terminal style 9. 



9. Face bare except on oral margin 10. 



Face pilose or hairy, more convex 11. 



(*) Ospriocerus diver sus Williston (Mexican) has a small style. 



TRANS. AM. ENT. SOC, XXXV. APRIL, 1909. 



