86 NORTH AMERICAN DII'TERA. 



25. Front tibias distally and tarsi of the $ dilated, those of the female 



slightly widened. . . Platychirus St. Fargeau and Serv. 



Front tibiae and tarsi slender in both sexes. Melanostoma Schiner. 



26. Abdomen narrowed toward the base, in outline spatulate or club- 



shaped. ........... 27 



Abdomen oval or slender, not club-shaped or spatulate. . . •)\ 



27. Third longitudinal vein deeply curved into the first posterior cell (Cen- 



tral and South America). . . . Salpingogastek Schiner. 

 Third longitudinal vein straight or gently curved. ... 28 



28. Hind femora slender ; front of female long, narrowed above. . 29 

 Hind femora thickened; abdomen less elongate; front not long and 



narrow above. .......... 30 



20. Alula? rudimentary or wanting. . . Bacchina Williston, nov. 



Alula? well developed Baccha Fabricius. 



30. Epistoma produced anteriorly, the face in profile deejjly concave from 

 antenna? to tip ; third joint of the antenna; rounded. 



SiMiEGiNA Meigen. 



Epistoma produced more downward, in profile gently concave; third 



joint of the antenna? not rounded. . . Neoascia Williston. 



ol. Front long, much narrowed above in the female; cheeks very narrow, 



the eyes approaching each other at the lower part of the head ; wings 



usually with a dark ])icture; abdomen more or less elongate. 



( )cYi'TAML'S Macquart. 

 Species without the above characters. ...... 32 



32. Dorsum of the thorax with yellow lateral margins. . . . 39 

 Dorsum of thorax not with 3'ellow lateral margins. . . . 33 



33. Abdomen with definite yellow cross-bands. ..... 34 



Abdomen not with definite yellow cross-bands. . ... 42 



34. Hind femora extraordinarily thickened. Syritta St. Farg. and Serv. 

 Hind femora slender. ......... 3i) 



35. Sixth abdominal segment in the $ as long as tlie two preceding to- 



gether, cylindrical ; fifth segment in the J one-half as long as the 

 preceding. ...... Eupeodes Osten Sacken. 



Sixth segment not peculiar, the fifth segment of the 9 one-third or t>iie- 

 fourth as long as the preceding. ...... 3(5 



3fi. Front very convex ; eyes of $ with an area of enlarged facets above. 



Cataromua Osten Sacken. 

 Front not remarkably convex. ....... 37 



37. Third longitudinal vein with a distinct curvature into the first posterior 

 cell; third joint of the antenna; elongate oval. Didea Maciniart. 

 Third longitudinal vein straight or gently curved; epistoma not pro- 

 duced (if ]>roduced snout-like, Ii/iiii(/iii). . . . . oS 



