North Amkrican Diptera. 51 



33. Hind femora thirkoned. ....... 34 



Hind femora slender. 37 



34. Species wholly or cliiefly reddish or lutescent. . . . 30 

 Black species, sometimes with luteous spots on face, humeri, 



basal angles of abdomen, etc 35 



35. Scutellum unusually large, nearly square in outline; males 



dichoptic Chalcomyia 



Scutellum not unusually large, considerably broader at the base; 

 males holoptic Myioleita 



36. Face carinate ; abdomen oval Brachyopa 



Face produced, obtusely tuberculate. Hammersciimidtia 



37. Epistonia produced into a long porrected snout. . Riiingia 

 Epistoma not at all produced Chilosia 



38. Third longitudinal vein bent deeply into the first posterior 



cell 40 



Third vein not deeply bent into the first posterior cell ; antennifi 

 elongate 39 



39. Arista feathery plumose Volucella 



Arista very densely plumose, appearing like a solid mass. 



Cope STY LDM 



40. Hind femora with sharp tooth-like projection below near the 



outer end ; large species Milesia 



Hind femora without tooth-like projection below. . . 41 



41. Frontal triangle of male strongly protuberant. Doliosyrphus 

 Frontal triangle not protuberant. ..... 42 



42. Thorax with distinct yellow markings; femora thickened ; hy- 



popygium large Pteroptila 



Thorax without distinct yellow markings; hind femora occa- 

 sionally thickened ; hypopygium not prominent Ekistalis 



43. Arista plumose. 44 



Arista bare or pubescent 45 



44. Thinly pilose, abdomen with yellow bands. . Sbricomyia 

 Thickly pilose, abdomen without yellow. . . Arctophila 



45. Third longitudinal vein bent deeply into the first posterior cell • 



hind femora thickened 4(5 



Third vein only gently curved 51 



46. Face with a sharp longitudinal ridge in the middle ; hind fem- 



ora with an angular protuberance below near outer end. 



Tropidia 



