78 NOKTII AMERICAN DIPTEKA. 



/r^-~^cx -,^,^ ,^. ,,. ■■ ,,, 



4. Face wide, frbnt deeply excavated. . 6ii.AJ*PTOPSH;OPiTS Aldrich. 

 Face narrow, front scarcely excavated. . Ekptokhethum Aldricli. 



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



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



Plagioxkurus Loevv. 

 Posterior cross-vein nearly transverse, usually no apical cross-vein. (3 



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. 



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



I^OLiciioinis Latreille. 



8. llypopygium long, extending forward under the venter. . . D 

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



0. Arista short-plumose 10 



Arista pubescent or bare. ........ 12 



10. Fourth vein beyon<l the jxisterior cross-vein gradually convergent 



toward the third PofcCH.-mK miuTJS M \ h :\^y 



Fourth vein shortly before the tip quite sud<lenly bent toward the ^ 

 third.* . ." 11 ' 



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



Pelastoneurds Loew. 

 Hypopygium sessile, with long, branching appendages. 



M£x^£M>AmuivKtKUb Aldiich. 



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



lowed out, or at least flattened down to a ])lane. . . . 1-j 

 Before the scutellum convex as usual. IB 



i;>. Hypopj'gium 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 cjiiefly metallic, sometimes dusted ; legs very long. 



di-'h. 



* If with a marked concavity toward the apex, see Paracdius, in whi<'li 

 tlu' ])ultescence of the arista is rather strong. 



