AQUATIC INVERTEBRATE FAUNA OF WYOMING AND MONTANA. 
241 
hairs moderately robust, the first segment not longer than the second. No emargi- 
nation separating head from body, but the dorsal surface very slightly sinuate there. 
Abdominal processes all distinct, anterior much the longest. Caudal claw with 
accessory teeth, about six in number, the three proximal the largest. Anal spines 
about ten. Posterior spine of the shell given off from the middle of the valves, in 
the adult female a third to a half as long as the valve. Shell moderately coarsely 
marked in quadrangular areas, the lower and dorsal margins spinulose from the 
middle backwards. Length 2 millimeters, depth 1 millimeter. 
Heart Lake, Yellowstone Park, Wyoming. 
Daphnia thorata, n. sp. 
This species belongs to the hyalina group, and may possibly be entitled only to 
varietal rank. The distinctness and constancy of its characters, however, in collec- 
tions made by us in Flathead and Swan lakes in western Montana, and the number 
of minor points in which it differs from liyalina , as most recently described, lead 
me to distinguish it here as a specific form. 
It is oval in outline; the long and slender posterior spine is placed at or a trifle 
above the middle; the length of the head is about a third that of the valves of the 
shell excluding the spine, and there is no trace of dorsal emargiuation between head 
and body. The head is narrowed toward the base and elongated forward in a way 
to give it the outline of a high bell jar with a flaring base. Its front is broadly 
and regularly rounded, its ventral margin usually conspicuously concave and closely 
like the dorsal, although occasionally the head is straight or convex beneath. The 
posterior margin is either straight or slightly concave, and the beak stands free from 
the front margin of the valves, and by its extension downward not only covers the an- 
tenna 1 but reaches clearly beyond the tips of the sensory hairs. The eye is of medium 
size, placed far back of the front of the head and equidistant from the tip of the beak 
and the dorsal junction of the head and body. The pigment speck is of moderate size, 
placed directly behind the eye, and much farther from it than from the posterior mar- 
gin of the head. 
The antenn® are moderately stout, entirely smooth except for inconspicuous trans- 
verse rows of minute appressed hairs upon both peduncle and rami, and a row of 
short, tooth-like spinules at the distal end of each segment. The swimming hairs are 
rather slender, the second joint commonly decidedly shorter than the first. 
Fornices slight, arising above and a little behind the eye and terminating directly 
behind the antenn®, above the bases of which they project but slightly. The lower 
margin of each valve is set with the usual spinules almost to the beak, and the dor- 
sal margin is similarly armed for a distance in front of the spine about equal to half 
the length of the latter. The valves are marked off by fine lines into large quadrate 
meshes. 
The dorsal abdominal processes rise separately, the two anterior, however, in 
immediate contact at their bases. The first of these is decidedly the longer, but the 
third process is distinct, although low. The anal set® are two-jointed, the second 
joint the shorter. The abdomen is regularly narrowed backwards, and the anal 
groove is provided with twelve to fifteen teeth on each side, commonly the latter 
number. The termiual claws are without accessory comb. The intestinal coeca are 
short, not longer than the diameter of the eye, and extend directly forward. 
F. C. B. 1891—16 
