[3] LAKE SUPERIOR ENTOMOSTRACA. 703 



northern regions of Europe and of America was more immediate than 

 now — a time, that is, when the lands of the northern hemisphere were 

 more closely connected or less widely sterilized by ice. 



The typical form of sicilis is larger than gracilis, females ranging 

 from 1.3 to 1.6 mm in length, without the caudal seta3, while gracilis does 

 not commonly surpass l mm . The fifth and sixth segments of the ceph- 

 alothorax are very imperfectly divided (no suture being apparent on 

 the back), aud the last segment is more deeply emargiuate behind than 

 seems to be the case with gracilis. There is a single very miuute spine 

 at the tip of the lateral lobe of this segment, aud sometimes a still more 

 minute one some distance below and within this, on the inner inferior 

 part of the lobe. 



In ovigerous females the abdomen has three segments, besides the 

 furca, of which the first is as loug as the second aud third — the second 

 being the shortest, but still nearly equaling the third. The furca is, in 

 the female, a little longer than the third segment, *in the male much 

 longer than the second, the second, third, and fourth abdominal seg- 

 ments in the latter sex being almost exactly equal, and the first a little 

 shorter. 



The basal joint of the legs of the fifth pair (PI. i, fig. 6,) bears, in both 

 male and female, a large cyliudrical process, ending with a stout spine or 

 spine-like tip. In the female, the third joint of the outer ramus is scarcely 

 distinguishable as such, being merely a stout spine or hair articulated at 

 the base aud without accessory hairs or spiues. The large process of 

 the second joint is slightly curved outward. The inner ramus has two 

 long, strong diverging spines, half as long as the ramus, near its tip, 

 this extending beyond their insertion as a smooth, obtuse triangle. 

 Left leg of male without spine on second basal joint or terminal seta on 

 outer ramus. Inner rami of both legs smooth at tip, one- or two jointed. 

 Outer ramus of left leg distinctly two-jointed, the segments equal, the 

 tip a rounded cushion covered with delicate short hairs. A similar 

 hairy pad at middle of inuer surface of this segment. 



In specimens taken August 9 at Marquette, spots of vivid red about 

 the mouth aud at the posterior fourth of the cephalothorax were com- 

 monly connected by an indigo-blue or pale red stripe, which included 

 the alimentary canal and often adjacent structures. The ovaries were 

 also ofteu blue, sometimes very bright. Occasionally one was seen with 

 much more red irregularly distributed in the center of the body, aud 

 it is probable that earlier in the season red was the prevailing color. 

 The agg masses of the female were blue, varying to red; the eye dark 

 red ; the abdomen colorless ; and the thoracic legs of a bluish tint. 



D. sicilis, var. imperfectus, new var. 



Occurring commonly with the form above described is another (often 

 certainly adult, as shown by the developed spermatophore in the male 

 and the external egg masses in the female) much smaller in average size, 

 and with the terminal hook of the fifth pair of legs of the male thicker, 



