46 NORTH AMERICAN DIPTERA. 



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



hence contiguous with the discal cell. ..... 4 



The last posterior vein arises from the second basal cell. . . 5 



4. Third joint of the antennae with a long, delicately fringed, lamelliform 



style ; usually large, more or less elongated species ; males dichoptic 



(Hermetiina^) IIermetia Latreille. 



Third antennal joint not with such a style ; abdomen short. 



CUTELLARIN^. 



5. Antenna; with a slender dorsal or terminal, bare or pubescent arista. 



Sargin^. 

 Antenna? never with a slender or long arista. . . Stratiomvin^. 



BEKIDIN.^. 



1. Three posterior veins, all arising from the discal cell.* . . 2 

 Four posterior veins, all arising from the discal cell; scutellum with 



spines. ........... 6 



2. Scutellum without s])ines. ........ 3 



Scutellum with spines. ......... 4 



3. Short, small species. .... Allognosta Osten Sacken. 

 Elongate, larger si)ecies ; head sometimes small. (Central and South 



America). ...... Chiromyza Weidemann. 



4. Scutellum with ten spines (Central and South America). 



Heteracantha Schiner. 

 Scutellum with not more than six spines. ..... 5 



5. Head hemispherical Beris Latreille. 



Head not hemispherical, the front much flattened and elongate (Central 



America). Berismyia Giglio-Tos. 



(■>. Occiput flattened; hind femora simple; the last two abdominal seg- 

 ments small ScoLioPELTA Williston. 



Occiput excavated ; hind femora thickened at the extremitj'. 



Neoexaireta Osten Sacken. 



sargin.t:. 



1. Antenna; elongate, witli a terminal, pubescent st3'le (Central and South 



America) Ackoch.eta Wiedemann. 



Antenna* short with an aj)ieal or preapical arista 2 



2. Scutellum with two s])ines (Central and South America).! 



Rhaphiocera Wiedemann- 

 Scutellum without spines. 3 



* Variable in Beris. 



t If but a single submarginal cell present, compare Notliomii'id (Stra- 

 tiomj'ina* ?). 



