242 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



Length, 2 millimeters to '2.5 millimeters; depth half the length, sometimes a 

 little more. Length of spine somewhat variable, but commonly about equal to the 

 depth of the sheik 



Described from females only. 



Abundant in Swan and Flathead lakes, Montana. 



Daphnia pulex, var. pulicaria, n. var. (Plate xxxvn, Fig. 1.) 



Similar, especially in the female, to typical D. pulex, to which it is closely re- 

 lated by its more general characters. Body a broad oval, moderately thick, colorless, 

 commonly without dorsal emargination between the head and thorax, although some- 

 times in the generation of females bearing ephippia there is a broad concavity just 

 above the heart. The lower border of the head is broadly concave and the beak is 

 long and applied against the anterior margin of the shell. Moderately long posterior 

 spine placed above the middle line; caudal claws with two sets of teeth, and with 14 

 to 1 7 curved spines at the anal furrow. 



The head of the female is small, somewhat depressed, crested, as in D. pulex, the 

 crest extending backward to the middle of the dorsnm; fornices terminating pos- 

 teriorly opposite the heart, and extending anteriorly to the eye. The beak projects 

 a little beyond the tips of the sensory hairs; the eye is large, its vertical diameter 

 contained scarcely twice in the distance from the eye to the tip of the beak, placed 

 close to the broadly rounded anterior margin of the head, and provided with many 

 large lenses. Pigment speck of moderate size, midway between the eye and the 

 posterior margin of the head. 



Antenme but moderately developed, destitute of scale-like appendages like those 

 ofpule.r, but set with inconspicuous transverse rows of rather slender hairs. Swim- 

 ming hairs moderate and moderately feathered, three-jointed, the third segment 

 very short, but evident. The coecum of the intestine strongly curved, extending at 

 first obliquely downwards towards the middle of the eye, and then turning almost 

 directly upward at an acute angle, terminating midway between the middle of the 

 upper margin of the eye and the front of the base of the antenna. The surface of the 

 valve is marked with quadrate areolations, and the margins, both dorsal and ventral, 

 are provided with backward-projecting spines or thorns as far as the middle. The 

 anterior half of both margins smooth. The posterior spine is variable in length, 

 reaching in adult females a fourth the entire length of the head and body. 



Dorsal processes of the abdomen distinct, the two anterior contiguous in their 

 origin, not united at their base, the first the longer, smooth, and directed forward, 

 the second hairy, turning backward. Two others -in the form of low elevations, the 

 last inconspicuous, but both hairy. 



The abdomen is rather broad, the posterior margin broadly rounded, the ante- 

 rior margin straight; 13 to 17 spines bordering the anal furrow, length regularly 

 increasing from above downwards; the teeth of the caudal claw in two groups of 

 from four to six each, the upper group very much the smaller; the anterior margin of 

 each claw with two distant slight emarginations, as in D. pulex. 



Length of an adult female 1.9 millimeters without the spine; depth, 1.1 millimeters; 

 spine 0.5 millimeter. Female bearing ephippium, a little deeper (1.2 millimeters). 



The male smaller, narrower, with head more depressed, the dorsum especially more 

 nearly straight, and the posterior spine standing higher, continuing the line of the 

 dorsum backwards. The lower margin of head is only slightly concave, the posterior 



