62 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
the middle of the last segment. The margins of this process are 
smooth, but it is broad and emarginate at the tip. The fifth pair of 
legs of the male resemble the corresponding appendages of D. stagnalis, 
but differ notably in detail. The left ramus of the rigkt leg is borne 
at the inner terminal angle of the second joint, is longer than the 
joint following, is armed at the apex with a few small acute spines, 
and bears upon its outer margin, near the tip, a broad fascicle of 
delicate hairs. The basal joint of the outer ramus is two-thirds the 
length of the second joint of the peduncle, and without hairs or spines 
of any description. The second joint of this ramus is about equal in 
length to the second joint of the peduncle, and bears at its outer mar- 
gin, close to the tip, the usual stout seta, which is two-thirds as long 
as the joint to which it is attached. The terminal claw is not regu- 
larly curved, but is nearly straight for the basal three-fourths. The 
left leg is bi-ramose, the inner ramus straight, slender, extending 
about to the middle of the second joint of the outer, and armed at its 
tip. The second joint of this ramus is as long as the first, if measured 
from the tip of the apical spine. This spine, seen from behind, is 
stout, conical, rather blunt, and has opposed to it within, projecting 
from the inner angle of the segment, a stout, curved seta, slightly 
plumose on its distal half. Between these, but more closely applied 
to the outer spine, is a hemispherical cushion-like elevation, set with 
small, short spinules. On the basal half of the inner margin of this 
terminal segment is also a much larger hemispherical cushion, but 
with longer and more slender hairs, while the terminal half of the in- 
ner margin of the segment preceding is also moderately inflated and 
covered with delicate hairs. The antenne of the female are 25-jointed, 
as usual, and reach to the base of the abdomen. The legs of the fifth 
pair closely resemble those of stagnalis, but have the terminal setie of 
the inner ramus much less developed. This ramus is a little shorter 
than the basal joint of the outer ramus, and about half its diameter. 
It bears at its tip two stout sete equaling the ramus itselfin length, 
plumose under a high power, and has, in addition at its inner tip and 
on the margins adjacent, a patch of delicate hairs and spines. The 
second joint of the outer ramus is as long as the first, if measured 
from the tip of its terminal claw. The latter is nearly straight, very 
slightly recurved. This joint bears a single spine at its outer distal 
angle, just within which is the rudiment of the third segment of the 
ramus, which bears two spines similar to the above, the inner of which 
is the longer, the outer itself being longer than the adjacent spine of 
the second joint. Adults of both sexesare blood-red throughout, except 
the egg sac of the female, which is purple.’’ Length of female, in- 
cluding setie, 5.1 mm.; male, somewhat smaller. In various lakes in 
Yellowstone Park. 
