4 AMERICAN DIPTERA. 



rowed or closed apically ; anal cell large, sometimes with a long 

 attenuated lobe. 



This genus, at present, holds two very characteristic groups. If, 

 upon further study of those species not herein mentioned, these 

 groups still hold their well-marked characters, they may be, with 

 safety, considered ^ood genera. I have, in the following table — 

 which treats only of those species under observation — made these 

 groups the primary divisions. The difference in form of the geni- 

 talia of % and ovipositor of 9 seems to be the most marked char- 

 acter for their separation. These differences, as well as their specific 

 variations, I have shown, when they exist, by a series of sketches. 

 Those instances where only the clasps of the male are figured, the 

 other parts are similar. 



Front narrow, more than twice as long as wide; the ocellar tubercle nearer the 

 occiput than to the antennje ; thorax more or less well developed an- 

 teriorly, the humeral calli distinct; the genitalia much developed; 

 the clasps of male, usually situated beneath the third abdominal seg- 

 ment, are membraneous and sessile, greatly enlarged, not filiform ; 

 the ovipositor of female shorty and irregularly developed, truncate at 

 apex, not extending forward beneath the abdomen 1. 



Front nearly as wide as long; the ocellar tubercle about midway or nearer the 

 antennte than to the occiput; thorax much constricted anteriorly, the 

 humeral calli indistinct; the genitalia not unusually enlarged; the 

 clasps of male situated nearer the apex of abdomen on a more or less 

 elongated pedicle or common base, somewhat filiform; ovipositor of 

 female long, tapering to a more or less filiform apex, and extending 

 forward beneath the abdomen 2. 



1. Thorax and abdomen yellow or rufous, with a black median stripe, whicli is 



sometimes indistinct on the thorax uuivittti. Walk., "J) , 9 . 



Thorax and abdomen, except the clasps of male, entirely black. 



alesia Walk., '^,9. 



2. Wings uniformly blackish, not banded ; the costa, between the ends of second 



and third veins, much less than half tlie length of the last section of 



fourth vein (liversa Schi., 9- 



Wings hyaline or banded; the costa, between second and third veins, nearly 

 as long as the last section of fourth vein 3. 



3. Anal cell short, not much longer tlian the second basal cell 4. 



Anal cell more than twice as long as the second basal cell 6. 



4. Head and thorax ru fous 5. 



Head and thorax black; wings hyaline or faintly banded. 



am to nil lie !><>!<» Say, '^ , 9 • 



5. Wings with distinct cross-bands; hind femora with a jjreapicul ring; hind 



metatarsi wliite i'itiiiciata Fab., 9 • 



Wings with a di.scal brownish cloud ; liind femora and tarsi not so marked. 



iiebiiloMa Lw. ■£, 9. 



