THE SYRPHIDAE OF OHIO 75 



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

 tubercles on its border (Figs. 201, 202); a stump of a vein in the first posterior 



cell from the third longitudinal vein (Fig. 230) 10 



Small species; scutellum without spines; no slump of vein in first posterior 

 cell Pipiza (p. 81) 



10. Abdomen much narrowed at the base 11 



Abdomen not or but little narrowed at base Microdon (p. 79) 



1 1 . 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 spinous 



bristles below {Leprotiiyia) Lepidostola 



Body not clothed with flattened tomentum; the femora not thickened with spinous 

 bristles below 13 



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



face and front not wrinkled Paragus (p. 82) 



Front and face wholly black in ground color {Chrysogaster, Rhysops). ..... 19 



14. Face black in ground color 15 



Face more or less yellow or yellowish in ground color 26 



15. Abdomen only with four visible segments, very convex, the venter excavated; 



first two joints of the antennae very short, the third large, subquadrate, with 



a short subterminal arista Nausigaster 



Abdomen with more than four visible segments (Figs. 71, 151) 16 



16. Hind femora distinctly thickened (Fig. 212) 17 



Hind femora but little or not at all thickened 18 



17. Scutellum unusually large, nearly square (Fig. 203); males dichoptic 



Chalcomyia (p. 83) 



Scutellum not unusually large, considerably broader at its base; males holoptic 

 and with a facial tubercle Myiolepta (p. 83) 



18. Face rounded, not tuberculate, the oral margin not projecting Pipiza (p. 81 ) 



Face tuberculate or the oral margin projecting 19 



19. Epistoma projecting (Fig. 209); small, black species 20 



Face tuberculate, the oral margin not projecting (Fig. 243) ." . 21 



20. Front in the female and usually the face in both sexes with transverse wrinkles, 



(F'ig. 210); spurious vein obsolete; antennae short or long. Chrysogaster (p. 80) 

 Front and face not wrinkled; face pilose Psilota (p. 81 ) 



21. Metallic green, metallic green and black, or black species; facial orbits separated 



by a slender parallel groove (Fig. 220) Chilosia (p. 82) 



Black with more or less metallic green or blue, with yellow, yellowish or metallic 

 cross-bands on the abdomen; face not with orbital grooves 22 



22. Face with transverse grooves in the middle; (antennae elongate) Rhysops 



Face not with transverse grooves or wrinkles 23 



23. Wings not longer than the abdomen; ocellar tubercle large; abdomen depressed, 



long elliptical, somewhat narrowed toward its base, the markings ferrii.yinous 



or yellowish orange Pyrophaena 



Wings longer than the abdomen with yellow or greenish-yellow, or shining 

 metallic cross-bands; usually elongate species 24 



