84 NORTH AMERICAN DIPTERA. 



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

 have introduced at the close an auxiliary table or grouping of 

 a considerable number of the genera whi(;h can be defined by 

 decisive characters. 



TABLE OF GENERA. 



1. Antennae with a terminal style. 2 



Antenna with a dorsal arista. ....... 4 



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



Sphyximorpha Rondani. 

 First two joints of the antenna; short. 3 



o. Eyes bare, small species. .... Pelkcockha Meigen. 

 Eyes pilose, larger species Cali.icera 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. ........ G 



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

 oblique. 55 



(). Antennse elongate. 7 



AntenniB short. . 10 



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



men always with distinct yellow bands. Chrysoto.xum Meigen. 



Dorsum of thorax without 3'ellow lateral stripes or margins. . 8 



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

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



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



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

 terior cell from the third longitudinal vein 10 



Small species; scutellum without si)incs or tubercles; no such stump 

 of a vein present. Pipiza Fallen. 



10. Abdomen much narrowed near the base (Central and S. Anu>rica). 11 

 Abdomen not or but little narrowed nc>ar the base. ... 12 



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

 Face not swollen and })n)minent below. . Mixogasteu Macquart. 



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



Omecasykpius Giglio-Tos. 

 Second sei>nu'iit of the abdonu-n normal. ..... 1-3 



