April, 1911.] New Species of Diptera of the Genus Erax. 307 



NEW SPECIES OF DIPTERA OF THE GENUS ERAX. 



James S. Hine. 



The various species of Asilinae known by the generic name 

 Erax have been considered difficult for a long time. This largely 

 comes from the fact that the genus has not been treated with 

 reference to all the North American species included, but various 

 writers have described such species as have come to their atten- 

 tion in collections that have been made here and there throughout 

 the country. From the study we have made of various species 

 with a view to a treatment of the entire genus eventually we are 

 convinced that quite satisfactory characters are available for the 

 separation of the various forms when they are assembled so that 

 careful comparison may be made. But until that time comes 

 students may depend upon it that they will have abundance of 

 trouble in their attempts at determining these rather large and 

 attractive insects, even though they may appear easy to one 

 unacquainted with them. 



In western North America there is a group of species of the 

 genus with two submarginal cells, the first of which is long, or 

 with its base distinctly anterior to the base of the second posterior 

 cell. In the male the abdomen is entirely or in large part silvery- 

 white pollenose and two or more of the segments are furnished 

 with long white hair which is parted at the middle and directed 

 outward. The costa is not expanded and a thoracic crest is never 

 present. 



Williston and Osten vSacken have named four species of the 

 group, stramineus, dubius, splendens and rapax and six others are 

 described in this paper. It seems that stramineus and rapax are 

 very much alike and I am not sure but that they are one species. 

 I have seen other undescribed species from the Pacific coast 



region. 



Erax rapax Osten Sacken. M\"stax straw-yellow, legs black 

 except the bases of the tibiae which are reddish, clothed with 

 abundance of straw-yellow hair and scattering black bristles. 

 Wings hyaline. Length 18 to 23 millimeters. 



Palpi black with straw-yellow hairs, beard pale yellow, occip- 

 ito-orbital and ocellar bristles black, face and front yellow polli- 

 nose. Thorax yellowish-brown pollinose with pale hairs on the 

 sides and black hairs and bristles on the dorsum, but the vestiture 

 of this region is somewhat variable and specimens occur with 

 these bristles and hairs partly 3^ellow. 



First two segments of the male abdomen colored like the tho- 

 rax, segments three to five silver white and, except seven, furnished 

 with white hair parted at the middle and directed outward; the 

 posterior part of the second segment may show a few white hairs 



