258 ERNEST A. BACK. 



pogon in Western Diptera very closely. I have found no 

 difficulty in running his type material in his keys which I have 

 used, enlarging only sufficiently to include new species, and 

 in so doing have taken care not to impair their value. 



As many of his species have never since been collected, and 

 as I have found by actual comparison with type material that 

 his descriptions are excellent, I have not hesitated to embody 

 them direct, with credit, in the text. My reasons for so doing 

 is that when a man has made a good description it seems a 

 waste of time for another to redescribe for the sole purpose 

 of appearing more original. 



The species, cerrussatus, nebulo, varipennis and gibber, es- 

 pecially the last three, are aberrant forms. I have allowed 

 them to remain in this genus for the time being, as I know of 

 no better place for them, and it seems unwise to erect new 

 genera for them at this time. 



In one day Osten Sacken captured thirteen species at Web- 

 ber Lake, Sierra Co., Cal., eleven of which were new; — which 

 shows the abundance of the species of this genus in the West. 



SYNOPSIS OF SPECIES. 



EASTERN SPECIES.* 



Scutellum flat, with very few indistinct hairs Uitatius. 



Scutellum convex, with long, distinct, erect hairs (with short 



white pile in alleni) 2. 



Third segment of antennas red, very pilose species. 



niarginalis. 



Third segment of antennas black 3. 



Tibiee and tarsi altogether black or dark chestnut 4. 



Tibiae and tarsi more or less reddish or yellow 5. 



Scutellum with long black pile lyratus. 



Scutellum with short white pile alleni. 



Tibiae red, the tips only black; the male with two large black 



spots on the wings biniaciila. 



Tibiae red at base only; the male without large black spots on 



the wings falto. 



* These species are reported more frequently from New England, 

 New York and New Jersey, although specimens have been taken as 

 far west as Minnesota; marginalis has been reported from Virginia; 

 bimacula has been taken in Las Vegas Range, N. M. 



5. < 



