()2 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. stag'tialis, 

 but differ notably in detail. The left ramus of the right 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 antennte of the female are 25 joiiited, 

 as usual, and reach to the base of the abdomen. The legs of the fifth 

 pair closely resemble those of stagnaUs, 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 setse equaling the ramus itself in 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 sexes are blood- red throughout, except 

 the egg sac of the female, which is purple." Length of female, in- 

 cluding sette, 3.1 mm.; male, somewhat smaller. In various lakes in 

 Yellowstone Park. 



