27S 



NORTH AMERICAN DIPTERA. 



5. Posterior angle of anal cell acnte, but scarcely prolonged lobe-like. 



12 

 Posterior angle of anal cell distinctly drawn out into a lobe. 6 



6. Front punctate or scrobiculate.* ...... 7 



Front smooth. .......... 10 



7. Scutellum flat, with sharp edges; fourth longitudinal vein strongly 



curved forward at its distal end; front coarsely rugose. . 9 

 Scutellum convex, rounded on its edges 8 



8. Stigma not unusually elongate. ..... TJlidia. 



Stigma elongate, about as long as the costal cell. Acrosticta. 

 Wings with cross-bands (18) Euphara. 



9. Third antennal joint elongate (17). . . Notogramma. 

 Third antennal joint not elongate. . . . Chrysomyza. 



10. Face distinctly projecting below; third antennal joint rounded at 



the end. 11 



Face retreating; third antennal joint with a sharp anterior angle. 

 (9) Chsetopsis. 



11. Third antennal joint twice as wide as long. . . Zacompsia. 

 Third antennal joint not twice as wide as long (16.) Euxesta. 



12. Body extremely slender. . . . . . . . 13 



Body not slender; face carinate Seoptera. 



13. Front only slightly projecting in profile; face oblique. 



Stenomyia. 



Front very much projecting, so that the head is conical and the 



face nearly horizontal (13) Eumetopia. 



RICHARDIIN^S. 



Mesonotum with bristles in the middle posteriorly only; femora 

 often armed and incrassate; first longitudinal vein bare; posterior an- 

 gle of the anal cell obtuse; costal vein usually broken just before the 

 termination of the auxiliary vein; auxiliary and first longitudinal 

 veins closely approximated, their tips near together. 



1. Femora all armed with spines. 3 



Front and hind femora only, with spines. . . Sepsisoma. 



Front and middle femora unarmed. 2 



All the femora unarmed 5 



* Smooth in Acrosticta bicolor Cresson. 



