6 University of Michigan 



known to me have the second submarginal cell so long as in 

 mystacciis. Usually this cell has its base almost exactly oppo- 

 site the base of the second posterior cell. Total length 25 to 

 27 millimeters. Macqiiart figures a wing of mystaceus in 

 Dipteres Exotiques, Supplement i, Plate 8, figure 10. 



Genus Asii^us 

 Asilus may be divided into two groups by the presence or 

 absence of a transverse row of bristles just before the apex 

 of each abdominal segment, clearly larger than the hairs com- 

 monly present on the abdomen. The group characterized by 

 the absence of these bristles is smaller than the other and the 

 species included from North America hardly can be said to 

 fall together naturally. Loew and others used this means of 

 grouping old world species and American students have 

 adopted it in this country, presumably because nothing better 

 has been suggested. Six North American species have been 

 included in the group and an undescribed species collected by 

 F. M. Gaige at Lake Cushman, Washington, is before me. 

 The following key is offered for separating these seven species : 



1. Large, bright-colored species, wings distinctly colored all over.. 2 

 Smaller, modest-colored species, wings nearly hyaline 3 



2. Body and legs black, wings uniformly rich yeWow ... .iiiidas Brauer 

 Body brown, legs pale brown, wings brown with the veins 

 margined with paler scriccus Say 



3. Scutellum with numerous upright, mostly white bristles on 

 its posterior part, female genitalia with a circlet of strong 



spines at the tip 4 



Scutellum with a row of black bristles on its margin, female 

 genitalia without a circlet of spines at the tip 5 



4. Upper forceps of the male genitalia protruding half their 



length beyond the other parts leucopogon Williston 



Upper forceps of the male genitalia not protruding beyond 



the other parts cacop ilogns Hine 



5. Third antenna! segments wide, widest at middle of its 



length, body with abundance of fine pile platyccras Hine 



Third antennal segments slender, nearly the same width 

 throughout, body with normal amount of pile 6 



