198 



NORTH AMERICAN DIPTERA. 



5. Antennae with a slender, terminal arista (4). . Damalis. 

 Antennae with or without a terminal style, the latter sometimes 



simulating antennal joints. ...... 6 



6. Only four posterior cells present; front very broad above; small 



species. Townsendia. 



Five posterior cells as usual. ....... 7 



7. Head narrow, about as high as broad; face narrow above, broader 



and swollen below, in large part covered with hair; large, elong- 

 ate species. ......... 7 



Head very obviously broader than high. . 10 



8. Antennas with a terminal style. ...... 9 



Third joint of antennae long, without visible style; fourth poste- 

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

 with or without red on the abdomen. . . Ospriocerus. 



9. Style more than a fourth the length of the third antennal joint; a 



row of trichostical bristles usually present; first posterior cell 



usually closed (Scleropogon] (6, 37). . Stenopogon. 



Style about one-sixth the length of the third joint; trichostical 



bristles usually absent. ..... Stenopogon. 



10. Fourth posterior cell closed in or before the margin of the wing, n 

 Fourth posterior cell wide open, rarely nearly closed. . 16 



11. Antennae much elongated, apparently composed of five joints. 17 

 Antennae less elongated; style of antennae small or vestigial, not 



simulating antennal joints. ...... 13 



12. Face bare except on oral margin; large or very large species. 12 

 Face hairy or bristly. ........ 14 



13. Vein posterior to the second posterior cell continuous or nearly so 



with the fourth vein beyond the discal cell, the last section of 

 the fourth vein oblique, closing or much narrowing the first 



posterior cell (7). Microstylum. 



Last section of fourth vein continuous in nearly the same direction 

 with the penultimate section, the first posterior cell not closed 

 or narrowed (38). ..... Archilestris. 



14. Abdomen cylindrical*, not narrowed at tip, elongate ; near the 



proximal margin of the second and third segments with a white 



* Compare here Sphageus; I do not know the genus and can not 

 locate it more precisely from the description. 



