240 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
DESCRIPTIONS OF SPECIES AND VARIETIES. 
CLADOCERA. 
Daphnia clathrata, n. sp. 
A species of moderate size, with short, deep head, medium to very long posterior 
spine, minute pigment speck, and pectinate tarsal claw. In the immature female there 
is a prominent angle just above the swimming antenme, like that of I). dentifera. 
In the adult female the head, measured vertically across the rostrum, is twice as 
deep as its length from the base of the antenna to the middle of the front. It is 
sharply keeled rather than crested, very broadly rounded, its lower margin very 
slightly convex or quite straight, and its rostrum well marked in the adult. 
The eye is close to the front, the transparent orbit reaching to the margin of the 
head, of medium dimensions, its antero-posterior diameter contained twice in the 
space between the eye and the posterior margin of the head. The pigment speck 
is very minute, placed behind the lower half of the eye and nearer the posterior 
margin of the head. The fornices are not prominent. Beginning midway between the 
antenna and the eye, they arch broadly above the base of the former, making an 
obtuse angle a little beyond the antenna, and continuing as a slight carina backwards 
and downwards for a little distance on the side of the valve. The ventral margin of 
the shell is more broadly arched than the dorsal, the latter being, in the immature 
female, nearly straight from the heart backwards. The valves are conspicuously 
quadrangularly reticulate, spinose on their lower edges nearly to the beak, and on 
the upper edge to the vicinity of the heart. The posterior spine is very long, straight, 
slender, spinose to the tip, contained in average cases not more than twice in the 
length of head and body without the spine. 
The antenme are rather short, about half as long as the distance from the poste- 
rior margin of the eye to the base of the posterior spine. The swimming hairs are 
two-jointed, the basal joint the shorter. The dorsal abdominal processes arise in 
immediate connection, but are not united at their base. The anal furrow has about 
a dozen teeth on each side, and the caudal claw has a comb of three or four conspicu- 
ous teeth at its base, besides a little group of smaller ones. 
Length of an ovigerous female, 1.7 millimeters to the base of the spine; the greatest 
depth, 0.85. 
The male was not seen. 
Occasional in Grebe Lake, Yellowstone Park. 
Daphnia arcuata, n. sp. 
Head helmeted, rounded in front, length one third that of the shell, front con- 
cave, beak produced, extending beyond the sensory hairs of the antennae. For- 
nices beginning above the eye and extending nearly to the middle of the back, not 
especially produced above the antennae. Eye small, about midway between the man- 
dibles and the front of the head, and about midway between the tip of the beak and 
the dorsal surface of the head. Pigment speck very small, less than half the diam 
eter of a lens of the eye, and placed midway between the eye and the posterior margin 
of the head. The hitter concave, the beak extending backward and applied against 
the margin of the shell. Swimming antenme reaching the middle of the shell, their 
