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 shell. 
Described from females only. 
Abundant in Swan and Flathead lakes, Montana. 
Daphnia pulex, var. pulicaria, n. var. (Plate xxxvii, Fig. 1.) 
Similar, especially in the female, to typical I), 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 17 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 dorsum; 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 
of pulex, 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 back ward- 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 I), 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 
