t 68 NORTH AMERICAN DIPTERA. 



TABLE OF GENERA. 



1. Abdomen with seven visible segments.. .... 5 



Abdomen with five or six visible segments. .... 2 



2. Three posterior veins, all arising from the diseal cell. . . 38 

 Four posterior veins, the first and third sometimes vestigial Imt 



at least represented by angulations of the diseal cell. . 3 



3. All the posterior veins arise from the diseal cell, the fifth ]K>steri<>r 



cell hence contiguous proximally with the diseal cell. . 29 

 The last posterior vein arises from the second basal cell. . 4 



4. Antenna- with an elongate terminal or dorsal arista. . . 11 

 Third antenna! joint not with a distinctly differentiated arista, its 



segments homologous or nearly so. . . . . . 20 



HKRIDIN.K. 



5. Three posterior veins, all arising from the diseal cell.* . b 

 Four posterior veins, or vestiges of them, all arising from the dis- 

 eal cell; scutellum with spines. ...... 10 



6. Scutellum with spines. ....... 8 



Scutellum without spines. ....... 7 



7. Short, small species; third vein with an anterior branch (33). 



Allognosta.' 

 More elongate and larger species, especially in the female; third 

 vein simple (1) Chiromyza. 



8. Scutellum with ten spines. .... Heteracantha. 

 Scutellum with less than ten spines. ..... 9 



9. Head hemispherical (2,3) Beris. 



Head not hemispherical; the antennae situated low down, the 



frontal region long and plane Berismyia. 



10. Hind femora thickened. ..... Neoexaireta. 



Hind tibiae thickened at extremity. t .... Actina. 



The third vein rarely arises from the basal cell in species of />'<•> is. 



t The genus . Icltna, to which Herts viridis has been referred, has a 

 dichoptic head in the male, four posterior veins arising from the dis- 

 eal cell, thickened distal extremity of the tibiae, etc. Osten Sacken 

 has given as the chief distinction of the genus from Juris the well- 

 developed palpi, vestigia] in Hois. In our spu-ii-s of Ren's, how- 

 ever, the palpi are of considerable size. Beris viridis differs from 

 other species of the ^ciius in having dichoptic eyes in the male; hut 

 its venation is typically that of Hn is. 



