AMERICAN DIPTERA. 157 



SYNOPSIS OF SPECIES*. 



1. Empodia absent 2. 



Empodia present 3 . 



2. Hind femora with one large yellow band on its swollen portion; 



hind tibiae five-banded; second posterior cell hardly longer 



than the third aiiiiulatus. 



Hind femora with two distinct yellow bands on its swollen por- 

 tion ; hind tibiae four-banded ; second posterior cell con- 

 siderably longer than the third sclieeft'eri. 



3. Anterior intercalary vein forming a distinct angle with that por- 



tion of the posterior cross-vein that closes behind the 



second posterior cell (PL 2, fig. 6) 4. 



Anterior intercalary vein not forming a distinct angle, but appears 

 more or less continuous with that portion of the posterior 

 cross-vein that closes behind the second posterior cell (PI. 

 II, fig. 7) 11. 



4. Dorsum of thorax polished black; hind femora with a large 



median yellow ring on its swollen portion.. ..atridorsalis. 

 Dorsum of thorax not wholly polished black. 5. 



5. Dorsum of thorax with median and two lateral stripes polished 



blackt; ground color of thorax elsewhere pinkish but cov- 

 ered thinly with a white bloom virg^atiis. 



Dorsum of thorax not so ^z^-^- 



6. Color of body nearly wholly yellowish-red testacedii8. 



Color of body not as above 7. 



7. Penultinate fifth of the hind femora below with a conspicuous 



patch of white pile hirtipes. 



Hind femora without such a patch of pile 8. 



8. Fourth posterior cell petiolate at baseJJ 9. 



Fourth posterior cell sessile or subsessile ; very small species with 



white pruinose bands on abdomen; proximal portion of 

 swollen part of hind femora dark brown ; distal portion, 

 yellow; extreme apex, dark pictipes. 



* This key has been made from a limited supply of specimens of the 

 species included. I have omitted ochraceus and scapularis, which I 

 have never identified with certainty. All of the type material of 

 Loew, Coquillett and myself, run very well, as does the rest of the 

 material in my possession. I have never seen but one specimen of 

 brevicornis. The greatest difficulty will be found at couplet 3; in 

 some species the venation mentioned is inclined to be variable in 

 different or even in the same specimen, and it may be necessary to try 

 both 4 and 11 before placing the specimen in question. 



t Sometimes these vittge are reddish; see note under description of 

 species. 



jt The fourth posterior cell of pictipes is sometimes appreciably 

 petiolate. 



TRANS. AM. ENT. SOC, XXXV. MAY, 1909. 



