88 NORTH AMERICAN DIPTERA. 



52. Frontal triangle of $ strongly protuberant (Doliosyrphus Bigot, Central 



and South America). .... PRIOMERUS Macquart. 

 Frontal triangle not prominent. 63 



53. Epistoma produced into a long porrected snout (Central and South 



America). . . . '.. ' LYCASTRIRHYNCHA Bigot. 

 Epistoma not produced 54 



54. Thorax with distinct yellow markings ; femora thickened ; hypogygium 



enlarged (Pteroptila) MEROMACRUS Rondani. 



Thorax without distinct yellow markings; hind femora sometimes 

 thickened ; hypopygium not prominent. . ERISTALIS Latreille. 



55. Arista plumose .50 



Arista bare or pubescent . . 58 



56. Antennae elongated PHALACROMYIA Rondani. 



Antennae short 57 



57. Thinly pilose; abdomen with yellow bands. SERICOMYIA Meigen. 

 Thickly pilose; abdomen without yellow. ARCTOPHILA Schiner. 



58. Third longitudinal vein bent deeply into the first posterior cell ; hind 



femora thickened. . . . ... . . . . 59 



Third vein only gently curved. ....... 64 



59. Face carinate ; hind femora with an angular protuberance below near 



the outer end. TROPIDIA Meigen. 



Face tuberculate or arched, not carinate 60 



60. Abdomen much narrowed at the base (Central and South America). 



CERIOGASTER Williston. 

 Abdomen not narrowed at the base 61 



61. Antennae elongate (Mexico and Europe). PLATYNOCH^ETUS Wiedemann. 

 Antennae short 62 



62. Thorax and scutellum densely pollinose above. PTERALLASTES Loew. 

 Thorax and scutellum not densely pollinose above. ... 63 



63. Third joint of the antennae broad ; thorax not vittate. . . 67 

 Third joint of the antennas oval ; thorax usually vittate. . . 64 



64. Ocelli remote from each other. . . . ASEMOSYRPHUS Bigot. 

 Ocelli not remote from each other. . . HELOPHILUS Meigen. 



65. Thickly pilose species. MALLOTA Meigen. 



Thinly pilose ',.,.. 66 



