25 2 NORTH AMERICAN DIPTERA. 



TABLE OF GENERA. 



1. Antennae with a terminal style. ...... 2 



Antennae with a dorsal (rarely subterminal) arista. . . 4 



2. Antennae cylindrical, the first two joints elongated; first posterior 



cell with a stiimp of a vein (24) (Ceria) . Sphyximorpha. 

 First two joints of the antennae short. ..... 3 



3. Eyes bare; small species. ..... Pelecocera. 



Eyes pilose; larger species. ..... Callicera- 



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; almost always rectangular. ... 6 



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



usually oblique. . . . . . . . . -55 



6. Antennae elongate (if arista plumose, see 56). ... 7 

 Antennae short. ......... 14 



7. Mesonotum with yellow lateral stripes; large species, the abdo- 



men always with distinct yellow bands (23, 41). 



Chrysotoxum. 



Mesonotum not with distinct yellow lateral stripes or margins. 8 



8. Face rounded, not tuberculate, pilose; oral margin not project- 



ing. . . 9 



Face not evenly arched; tuberculate or the oral margin project- 

 ing. ........... 12 



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



spines or tubercles on its border; a stump of a vein in the first 



posterior cell from the third longitudinal vein. . . 10 



Small species; scutellum without spines; no stump of vein in first 



posterior cell (3O). . Pipiza. 



10. Abdomen much narrowed at the base. . . . . .11 



Abdomen not or but little narrowed at base (1) . Microdon. 



11. Face swollen and prominent below. . Rhopalosyrphus. 

 Face not swollen and prominent below. . . Mixogaster. 



12. Body clothed with sparse tomentum; all the femora thickened and 



with spinoiis bristles below (Lepromyia*} . Lepidostola. 



Body not clothed with flattened tomentum; the femora not thick- 

 ened with spinoiis bristles below. ..... 13 



13. Face partly or wholly yellow, tuberculate below, the epistoma not 



projecting; face and front not wrinkled (5, 7). Paragus. 



* The name Lepidostola Mik has slight priority over Lepromyia. 



