200 NORTH AMERICAN DIPTERA. 



More pilose species, the bristles few and hair-like; antenna; 

 springing from a convexity, the facial profile thence receding 

 to the tubercle, which is situated low down; abdomen short, 

 head rather narrow. ...... Dicolonus. 



21. All the tibiae and the hind femora with short, strong seta?. 



Ech.thod.opa. 

 Hind femora, at least, without such setae (12). . Dioctria. 



22. Abdomen slender; front broad anteriorly, very narrow behind, 



the ocelli far forward. Plesioma. 



Front not narrowed behind. ....... 23 



23. Face distinctly swollen in profile, gibbous. 24 

 Face flattened, or gently convex. ...... 25 



24. Rather or quite thickly pilose; the gibbosity of the face reaches to 



the base of the antennae; anal cell usually open. Cyrtopogon. 

 Thinly pilose, more pollinose species; the convexity of the face is 

 confined to the lower part; anal cell usually closed. 



Lasiopogon. 



25. Hind tibiae distally and the hind metatarsi much thickened. 26 

 Hind tibiae not or but slightly thickened distally; hind metatarsi 



not enlarged. ......... 27 



26. Head much broader than high, transverse, goggle-like in appear- 



ance; abdomen short; wings large (compare Metapogon) (36). 



Holcocephala. 



Head only moderately broader than high, not at all spectacle-like 



in appearance. ....... Holopogon. 



27. Abdomen with thick, recumbent pile above; thickly pilose spe- 



cies; antennae slender Pycnopogon. 



Abdomen not with such pile above. ..... 28 



28. Slender, nearly bare species; face perpendicular, straight or gently 



concave in profile, narrowed above, and bare, except on oral 

 margin. .......... 29 



Face gently rounded, not prominent below, in large part hairy, 

 and but slightly or not narrowed above. ... 30 



29. Thickly whitish pollinose ; abdomen flattened, usually reflected 



upward; third joint of antennae and the style both slender. 



Stichopogon. 



Less thickly pollinose; abdomen cylindrical, a little broader at the 



base; third joint of antennae short and broad, the style minute. 



"Habropogon". 



