222 NORTH AMERICAN DIPTERA. 



3. Anal cross-vein forming a distinct angle with the basal part of the 



anal vein ; proboscis rarely longer than head ; thorax often 

 large. ... ....... 4 



Anal cross-vein recurved and confluent with the anal vein, or form- 

 ing part of the posterior side of the anal cell; proboscis often 

 elongate, rarely projecting forward ; antennas usually three- 

 jointed Empidinse. 



4. Anal cell as long as the second basal, or longer, its outer angle 



acute. ........... 5 



Anal cell shorter than the second basal, its posterior angle obtuse 

 or the anal cross-vein perpendicular to the anal vein; proboscis 

 short, rarely porrect; thorax seldom excessively convex. 



Ocydromiinse 



5. The discal cell emits three veins; proboscis short, sharp and incurv- 



ed; thorax comparatively small; antennae three-jointed. 



Brachystomatinse. 



The discal cell emits two veins; proboscis rigid, projecting forward; 

 thorax greatly arched; antennae two-jointed. Hybotinse. 



TACHYDROMIIN^. 



1. Both the sixth vein and the anal cross-vein present, though some- 



times feeble. ....... .2 



Both the sixth vein and the anal cross-vein completely wanting. 3 

 The sixth vein wanting, the anal cross-vein present; marginal cell 



long along the costa; first basal cell shorter than the second; 



front femora thickened; eyes contiguous below the antennae; 



palpi small, with an apical bristle; humeri constricted from the 



notum (16,18). Tachypeza. 



2. Front and middle femora thickened; middle femora with a double 



row of spines below; middle tibiae ending in a sharp spur; palpi 



broad . Platypalpus. 



Femora not thickened; middle legs without spurs and with minute 

 or no spines; basal cells subequal. Symballophthalmus. 



3. First and second basal cells nearly equal; eyes widely separated; 



more or less pollinose species. ..... 4 



First basal cell much shorter than the second; eyes contiguous be- 

 low the antennae; shining species. .... 6 



4. Arista dorsal; wings less than one-third the length of the abdomen. 



Thinodromia. 

 Arista terminal or nearly so; wings surpassing the abdomen. 5 



