188 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
Daphnia atkinsonii Baird appears to us but a variety of this species. 
There is said to be no depression between head and body and the anal 
teeth diminish dorsad instead of being nearly equal as in D. psittacea. 
Considerable disagreement exists in the various descriptions. Daday’s 
figures show no grounds for separating the species. 
* Daphnia clathrata Forbes. 
Forbes ’93. 
‘A species of moderate size, with short, deep head, medium to very 
long posterior spine, minute pigment fleck, and pectinate tarsal claw. 
In the immature female there is a prominent angle just above the 
swimming antenne, like that of D. dentifera. In the adult female the 
head, measured vertically across the rostrum, is twice as deep as its 
length from the base of the antenne 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 
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 dis- 
tance 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 antenne are rather short, about half as long as the distance 
from the posterior 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 conspicuous 
teeth at its base besides a little group of smaller ones. Length of 
ovigerous female 1.7 mm. to the base of the spine; the greatest depth 
0.85 mm. The male not seen. Occasional in Grebe lake, Yellowstone 
Park.” 
