50 Everett E. Wehr 



tute of the usual clothing of villi, causing the wings to have a 

 glassy appeai'ance; hind femora a little shorter than two and 

 one-half times their width, and are held in longitudinal gi-oove- 

 like impressions of the abdomen during flight; chitinous parts of 

 sternites only one-third the entire width of the abdomen; head 

 subhemispherical, the eyes composing the greater part of the 

 head; face subcarinate Syritta 



Without the above conglomeration of characters 3 



3. Hind femora with an apical saw-tooth prominence; face sub- 

 carinate to carinate Tropidia 



Hind femora without a saw-tooth prominence; face not carinate 4 



4. Third vein with a downward loop into first posterior cell; 

 mesonotum ochraceous, very densely pollinose above Pterallastes 



Third vein straight or with a very gentle downward curve 5 



5. Epistoma abruptly truncate, face in profile deeply and evenly 

 concave; first posterior cell closed, petiolate Xylota 



Epistoma produced either well forward or protruding downward 6 



6. Antennae inserted on prominence slightly higher than vertex of 

 head; lateral margins of abdomen yellow Somula 



Antennae inserted below vertex of head; lateral margins of 

 abdomen not entirely yellow Cynorrhina 



7. Antennae inserted near middle of head; face not longer than 

 front Temnostoma 



Antennae long or short and inserted above middle of head on a 

 conical process; face much produced downwards; sixth vein 

 entering wing margin shortly beyond anal cell Sphecomyia 



Antennae inserted above middle of head; face not produced 

 downwards; sixth vein prolonged obliquely outward from anal 

 cell; hind femora with conical, tooth-like projection below near 

 distal end Spilomyia 



Syritta St. Fargeau and Serville 



Syritta pipiens (Linnaeus). Syst. Nat., 10th ed., 594 (1758) ; Williston, 

 Synop. N. A. Syrph., 240 (1886). 



156 



