7b OHIO BlOLOGlCAIv SURVEY 



24. Front tibiae distally and the tarsi of the male dilated, those of the female slightly 



widt-ned (Figs. 214-216 and 244) Platychirus (p. 84) 



Front tibiae and tarsi slender in both sexes 25 



25. Rather large, blackish species, with a large flat, elliptical abdomen. Xanthandrus 



More elongate and slender species, abdomen not elliptical in outline 

 Melanostoma (p. 85 ) 



26. Abdomen narrowed toward the base, distinctly club-shaped or spatulate in 



outline Fig. 217) , 27 



Abdomen oval or slender, not spatvdate or club-shaped in outline 30 



27. Third longitudinal vein bent deeply into the first posterior cell. . .Salpingogaster 

 Third longitudinal vein straight or gently curved (Figs. 151, 250) 28 



28. Hind femora slender; front of male long, narrowed above; the cheeks very 



narrow below the eyes; abdomen often very slender Baccha (p. 83) 



Hind femora thickened; front not unusually long in female 29 



29. Epistoma produced anteriorly, the face in profile deeply concave from antennae 



to tip; third joint of antennae rounded Sphegina (p. 88) 



Epistoma produced more downward, in profile gently concave; third joint of 

 antennae not rounded . . Neoascia (p. 89) 



30. Front long, much narrowed above in the female (Fig. 224); cheeks very narrow, 



the eyes approaching each other at the lower third of the head; wings usually 

 with dark picture; abdomen more or less elongate (compare Bacc/ia v/hen in 



doubt as to shape of abdomen) Ocyptamus (p. 84) 



Flies not having the above assemblage of characters 31 



31. Mesonotum with distinct yellow lateral margins (Figs. 64, 71) 38 



Mesonolum not with yellow lateral margins. 32 



32. Abdomen with definite yellow cross-bands 33 



Abdomen not with definite yellow cross-bands d2 



33. Hind femora extraordinarily thickened (Fig. 234) Syritta (p. 94) 



Hind femora slender (Figs. 1,71) 34 



34. Sixth abdominal segment in the male as long as the two preceding together. 



c^-lindrical; fifth segment of the female one-half as long as the preceding 



Eupeodes 



Sixth abdominal segment of the male not peculiar; the fifth segment of the 

 female one-third or one-fourth as long as the preceding 35 



35. Front very convex; eyes of male with an area of enlarged facets above 



( Lasiophthicus Cataboviba) Scaeva (p . 40) 



Front not remarkably convex 36 



36. Third longitudinal vein with distinct curvature into the first posterior cell (Fig. i) 



third joint of antennae elongate oval Didea (p. 85) 



Third longitudinal vein straight or gently curved (Fig. 151); epistoma not pro- 

 duced (if produced snout-like, Rhingia, p. 89) 37 



37. Males holoptic (Fig. 9) Syrphus ( p. S5) 



Males broadly dichoptic; arista more or less thickened Chamaesyrphus 



38. Mesonotum with median cinereous line; ocelli usually remote from the vertex 39 

 Mesonotum not with a median cinereous linear stripe 40 



39. Hind femora in the male thickened and arcuate, the tibiae dilated at the tip 



Toxomerus (p. 87 ) 



Hind fen;orasiinpleand straight; thetibiaenotdilated at tip. Mesogramma (p. 87) 



