84 NORTH AMERICAN DIPTERA. 



quent length of the table of the North American genera, I 

 have introduced at the close an auxiliary table or grouping of 

 a considerable number of the genera which can be defined by 

 decisive characters. 



TABLE OF GENERA. 



1. Antennae with a terminal style 2 



Antennas with a dorsal arista. 4 



2. Antennae cylindrical, the first two joints elongated (Ceria). 



SPHYXIMORPHA Rondani. 

 First two joints of the antennae short 3 



3. Eyes bare, small species. . . . . PELECOCERA Meigen. 

 Eyes pilose, larger species. . . . . " CALLICERA Panzer. 



4. Marginal cell of the wings closed and petiolate. . . . .48 

 Marginal cell open. . . 5 



5. Anterior cross- vein of the wings distinctly before the middle of the 



discal cell, rectangular. 6 



Anterior cross-vein near or beyond the middle of the discal cell, often 

 oblique. 55 



6. Antennae elongate 7 



Antennae short. . . .10 



7. Dorsum of thorax with yellow lateral stripes; large species, the abdo- 



men always with distinct yellow bands. CHRYSOTOXUM Meigen. 



Dorsum of thorax without yellow lateral stripes or margins. . 8 



8. Face rounded, pilose, not tuberculate; oral margin not projecting. 

 Face not evenly arched, tuberculate or the oral margin projecting. 14 



9. Moderately large to large species; scutellum flattened, usually with 



spines or tubercles on its margin ; a stump of a vein in the first pos- 

 terior cell from the third longitudinal vein. . . ' . .10 

 Small species; scutellum without spines or tubercles; no such stump 

 of a vein present. . . . , . PIPIZA Fallen. 



10. Abdomen much narrowed near the base (Central and S. America). 11 

 Abdomen not or but little narrowed near the base. ... 12 



11. Face swollen and prominent below. RHOPALOSYRPHUS Giglio-Tos. 

 Face not swollen and prominent below. . MIXOGASTER Macquart. 



12. Second segment of the abdomen with the lateral margins inflated. 



OMEGASYRPHUS Giglio-Tos. 

 Second segment of the abdomen normal. . . . . . 13 



