FAMILY SYRPHID.T: THE FLOWER FLIES 251 



7. Face perpendicular, with a swelling above; anterior crossvein at the 



basal fourth of the discal cell; antennae elongate and porrect; ab- 

 domen strongly constricted basally Mixogaster Macquart 



Face more or less tuberculate or carinate or the oral margin at least 

 slightly prominent 8 



8. All the femora with a patch of black setulae on their bases anteriorly; 



third vein strongly curved into the apical cell 91 



Posterior femora never with such setulae; third vein at most moder- 

 ately curved 9 



9. Arista plumose, rarely pectinate; legs never with bristles 10 



Arista bare or pubescent, if short plumose the legs bear bristles 1^ 



10. Apical crossvein recurrent 11 



Apical crossvein not recurrent, the apical cell never longest at its 



middle 15 



11. Face with three strong tubercles, one on either side of the median 



tubercle (76) *Ornidia St. Fargeau and Serville 



Face with only one tubercle or almost flat 12 



12. Arista bushy plumose, appearing moi'e or less strap-like (14, 65, 75). 



t Copestylum Macquart 

 Arista loosely plumose or pectinate 13 



13. Arista pectinate, the upper rays long, the lower ones extremely short. 



Volucellosia Cun-an 

 Arista plumose 14 



14. Eyes of the male widely separated, the front much longer than the 



face Megametopon Giglio-Tos 



Eyes of male contiguous, the front at most slightly longer than the 

 "face (12, 13, 26, 77) t Volucella Geofi^roy 



15. Facial side margins very distinct and extending almost to the base of 



the antennae 43 



Side margins not extending above the middle of the facial convexity. , 88 



16. Apical crossvein strongly recurrent, the first posterior cell longest in 



the middle and usually with an appendage at this point (66, 78). 



Citibaena Walker 

 First posterior cell not longest in the middle, the apical cell not 

 strongly recurrent 17 



17. Genitalia entirely concealed by the strongly convex abdomen when seen 



from the side; third antennal segment orbicular, very large; an- 

 terior crossvein situated before the middle of the discal cell (67, 79). 



Nausigaster Williston 

 Genitalia visible from lateral view; third antennal segment never 

 orbicular and abnomially large 42 



18. Antennae elongate and porrect; thorax and abdomen with bright yellow 



markings; wasp-like flies (23, 41, 82) §Chrysotoxum Meigen 



* Cuiran, 1930, Amer. Mus. Novit. No. 413, p. 2. 

 t Curi-an, 1930, Amer. Mus. Novit. No. 413, p. 3. 

 t Curran, 1930, Amer. Mus. Novit. No. 413, p. 6. 

 § Shannon. 1926, Pr. U. S. N. M., Ixix, Art. 11, p. 3. 



