April, 1911.] New Species of Diptera of the Genus Erax. 
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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 pollcnosc 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 Sacken 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. Mystax 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 IS 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 yellow. 
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 
