Syrphidae of Nebraska 19 



ton, Synop. N. A. Syrph., 29 (1886); Snow, Kans. Univ. Quart., 

 iii, 231 (1895). 



A s and $ from Lincoln, Lancaster County, April 20th 

 and 25th, 1908 (C. H. Gable). 



Syrphini 



Key to the Genera 



1. Abdomen elongate-slender and contracted beyond the base. ...Baccha 

 Abdomen not narrowed on basal portion 2 



2. Dorsum of thorax with yellow lateral stripes 3 



Dorsum of thorax without yellow lateral stripes 8 



3. Antennae very elongate, about six times as long as broad 



Chrysotoxum 



Antennae less than three times as long as broad 4 



4. Dorsum of thorax with a median cinereous line 5 



Dorsum of thorax without such line 6 



5. Hind femora of male thickened and arcuate, tibiae arcuate 

 and dilated at tip, hind femora of female posteriorly with black- 

 ened ring Toxomerus 



Hind femora and tibiae of male normal, hind tibiae of female 

 entirely yellow, rarely (var. bnscii) with blackened ring pos- 

 teriorly Mesogramma 



6. Eyes of male with an area of enlarged facets above; fourth seg- 

 ment of abdomen with two median yellow stripes and an oblique 

 side spot Allograpta 



Eyes of male not with an area of enlarged facets above; fourth 

 abdominal segment not so marked 7 



7. Face projecting below; slender species Sphaerophoria 



Face receding below; abdomen broadly oval Xanthogramma 



8. Third longitudinal vein deeply constricted into first posterior 

 cell ..Didea 



Third longitudinal vein straight or with a gentle downward 

 curve • ••. :: 9 



125 



