Diptera . 41 c 
flattened on dorsum, laterally sloping ventrad and mesad, armed along the basal 
two-thirds of its lateral margins with slender, slightly flattened hairs, and with 
four long, flat hairs on apical third, venter of apical segment with a large bifid 
protuberance. 
Length, 13 mm. 
Locality: Lake at Bernard harbour, Northwest Territories, June 26, 1915 
(F. Johansen). 
In the vial with the specimens is a large sack-shaped cocoon or pocket 
of a very tough consistency which may belong to this species. It is open at 
one end and shaped somewhat like the cocoon of Simulium except that it does 
not taper so much at bottom. The surface is coated in part with small pieces 
of rotten wood. 
SIMULIID^. 
There are several lots of larvae, pupse, and imagines of this family in the 
collection. The imagines, with few exceptions, are in very poor condition. 
The larva and pupa of one species, obtained at Bernard harbour, very closely 
resemble those of Simulium vittatum Zetterstedt, but as is shown in the text 
following it is specificially distinct. 
The larvae of this family are found only in running water, some species 
preferring very swift streams with rocky beds, and particularly those parts of 
the streams where there are falls or declivitous rock-surfaces over which the 
water moves at an accelerated speed. Other species are found in streams with 
only a moderate current, and since in these streams the bed is generally more 
or less muddy and gives an opportunity for a weedy or grassy growth, the 
larvae and cocoons are usually found attached to this growth or to roots or 
fallen branches of trees in the stream. 
The imagines are predaceous, usually feeding upon the blood of mammals, 
and are a great pest in certain parts of North America and Europe. As a general 
rule the flies do not bite man, but they cause great discomfort by flying precipi- 
tately against the face, and by getting into the hair. Their bite is more painful 
than that of a mosquito. 
There are imaginal representatives of two genera and three species in the 
collection. 
Prosimulium Roubaud. 
The only species of this genus in the collection is apparently undescribed. 
Prosimulium borealis, n. sp. 
Male. Black, opaque. Thorax and abdomen with yellowish white hair. 
Wings clear. Halteres brown. 
Head as in hirtipes Fries, the antennae rather slender, postocular cilia dark. 
Thorax with long, but not very dense, subdepressed hairs, those on posterior 
margin and scutellum longer than those on disc; mesopleura with a few long 
hairs near upper margin. Fore tarsus with basal joint slender, not so thick 
but 1-5 as long as basal joint of mid tarsus; basal joint of hind tarsus almost 
as thick as hind tibia, and nearly four times as long as second, not produced 
at apex; second joint thickest a short distance before apex, three times as long 
as its greatest diameter, and twice as long as third. Venation similar to that 
of pecuarum Riley, the radial vein with third branch thickened at apex but not 
distinctly furcate. 
Length, 3 mm. 
Type locality: Wollaston peninsula, Victoria island, summer, 1915 (D. 
Jenness) . 
