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, .ill arising from the discal cell. . . 38 

 Four posterior veins, the first and third sometimes vestigial but 



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



3. All the posterior veins arise from the discal cell, the fifth posterior 



cell hence contiguous proximally with the discal cell. . 29 

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



4. Antennae with an elongate terminal or dorsal arista. . . n 

 Third antennal joint not with a distinctly differentiated arista, its 



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



5. Three posterior veins, all arising from the discal cell.* . 6 

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



cal cell; scntellnm with spines. ...... 10 



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



Scutellnm 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. Scntellnm with ten spines. .... Heteracantha. 

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



9. Head hemispherical (2, 3) ....... Beris. 



Head not hemispherical; the antennas situated low down, the 



frontal region long and plane. .... Berismyia. 



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



Hind tibiae thickened at extremity.! .... Actina. 



; " The third vein rarely arises from the basal cell in species of Beris. 



t The genus Actina, to which Heris viridis has been referred, has a 

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

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

 has given as the chief distinction of the genns from Bens the well- 

 developed palpi, vestigial in liens. In onr species of Beris, how- 

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

 other species of the germs in having dichoptic eyes in the male; but 

 its venation is typically that of Beris. 



