32 Everett E. Wehr 



Hind metatarsi not extraordinarily thickened or dilated tristis 



Microdon coarctatus Loew. Cent., V, 47 (1864) ; Williston. Synop. ^i 

 A. Syrph., 6 (1886). 



Three 6 6 and one 9 from Sioux County, the latter speci- 

 men collected July 1, 1911 (R. W. Dawson). 



Microdon lanceolatus Adams. Kans. Univ. Sci. Bull., ii, 212 (1903). 



A $ taken at Warbonnet Canyon, Sioux County, in 1901 

 (M. A. Carriker). 



Microdon fuscipennis (Macquart). Hist. Nat. Dipt., i, 488 (1834); 

 Williston, Synop. N. A. Syrph., 4 (1886). 



A 9 taken at Neligh( Antelope County, June 22, 1909 (W. 

 Thompson). 



Microdon tristis Loew. Cent., v, 45 (1864); Williston, Synop. N. A. 

 Syrph., 6 (1886). 



One s and one $ from West Point, Cuming County, June 

 27, 1906 (P. R. Jones) and Halsey, Thomas County, June 1, 

 1906 (LBruner). 



Chilosinae 

 key to the genera 



1. Face entirely black 2 



Face more or le.ss yellow 10 



2. Oral opening broadly oval and without indentations; face very 

 gently and evenly convexed, completely covered with rather long, 

 loose pile 3 



Oral opening irregular in outline, having a dorsal directed in- 

 dentation at the front margin 6 



3. Face considerably broader at the oral margin than at the an- 

 tennae (if doubtful, compare Hoingia) Pipiza 



Face but little or not at all broader at the oral margin than at 



138 



