80 NORTH AMERICAN DIPTERA. 



27. Hind coxae witwout erect hairs on the outer side, third and fourth veins 



near the tip convergent HYPOCHARASSUS Nick 



Hind coxae with one or more erect hairs, third and fourth veins paral- 

 lel, wings wide. . .28 



28. Scutellum with smaller hairs on the disk besides the marginal bristles. 



LASIARGYRA Mik. 

 Scutellum bare, except for the bristles. . . ARGYRA Macquart. 



29. Posterior third of thoracic dorsum, before the scutellum, concave or 



at least distinctly flattened. . - 30 



Dorsum rounded as usual. 32 



30. Bristles of thorax yellow CHRYSOTIMUS Loew. 



Bristles black, rarely brownish 31 



31. Fourth vein parallel with the third beyond the cross-vein, or nearly so. 



XANTHOCHLORUS Loew. 



Fourth vein converging toward the third beyond the cross-vein, either 

 gradually or by a double curve Go back to 15. 



32. Wings elongate, the posterior cross-vein considerably beyond the mid- 



dle, less than its length from the apex of the fifth vein (Hydropho- 



rinae) 33 



Wings not elongate, cross- vein scarcely beyond the middle, more than 

 its length from the end of the fifth vein (if less, the hind metatarsus 

 shorter, than the following joint) 35 



33. Fore femora slender LIANCALCS Loew. 



Fore femora more or less incrassated, with spines below. . . 34 



34. Spines of fore femora very short, thoracic dorsum without well marked 



pollinose lines HYDROPHORUS Fallen. 



Spines of fore femora long, dorsum with pollinose lines. SCELLUS Loew. 



35. Outer appendages of the hypopygium long, filiform. 



NEMATOPROCTUS Loew. 

 Outer appendages not long and filiform. '..'-'. . . . 36 



36. Second antennal joint with a thumb-like projection along the inner 



side of the third (Synarthrus Loew). . . . SYNTORMON. 

 Not with such prolongation 37 



37. Eyes contiguous or nearly so below the antennae. ... 38 

 Eyes contiguous above the antennae. . . DIAPHORUS Meigen. 

 Eyes closest together at the level of the antennae, diverging above and 



below ; middle legs of male distorted. . CAMPSICNEMUS Walker. 

 Eyes not approximated. . 39 



