78 NORTH AMERICAN DIPTERA. 



4. Face wide, front deeply excavated. . GNAMPTOPSILOPOS Aldrich. 

 Face narrow, front scarcely excavated. . LEPTORHETHUM Aldrich. 



5. Fourth longitudinal vein bent forward, forming an apical cross-vein; 



posterior cross-vein very oblique, parallel to the margin of the wing. 



PLAGIONEURDS Loew. 

 Posterior cross-vein nearly transverse, usually no apical cross-vein. G 



6. Hind metatarsi with large bristles above 7 



Hind metatarsi without large bristles above 8 



7. Face in male reaching the lower corner of the eye. 



HYGROCELEUTHUS Loew. 

 Face in the male not reaching the lower corner of the eye. 



DOLICHOPUS Latreille. 



8. Hypopygium long, extending forward under the venter. . . 

 Hypogygium short, not extending forward under the venter. . 21 



9. Arista short-plumose 10 



Arista pubescent or bare 12 



10. Fourth vein beyond the posterior cross-vein gradually convergent 



toward the third POECILOBOTHRUS Mik. 



Fourth vein shortly before the tip quite suddenly bent toward the 

 third* . . ..-,'. ... . . . .11 



11. Hypopygium pedunculate, slender, without long, branching appendages 



PELASTONEURUS Loew. 

 Hypopygium sessile, with long, branching appendages. 



METAPELASTONEURUS Aldrich. 



12. Before the scutellum the posterior third of the thoracic dorsum is hol- 



lowed out, or at least flattened down to a plane. ... 13 

 Before the scutellum convex as usual. .:'-.. . . . 1*5 



13. Hypopygium long, pedunculated. 14 



Hypopygium short, sessile or nearly so. . . . . . 15 



14. Bristles of the thorax yellow. . . APHANTOTIMUS Wheeler. 

 Bristles black. MEDETERUS Fischer. 



15. Color of body yellow, sometimes with a little black. 



NEURIGONA Rondani. 

 Color of body chiefly metallic, sometimes dusted ; legs very long. 



DACTYLOMYIA Aldrich. 



* If with a marked concavity toward the apex, see Paraclius, in which 

 the pubescence of the arista is rather strong. 



