240 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



DESCRIPTIONS OF SPECIES AND VARIETIES. 



CLADOCERA. 



Daphnia clathrata, n. s]>. 



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 antennae, like that of D. dentifcra. 



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 autero-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 foruices 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 antenna; 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 antenna?. 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 latter concave, the buak extending backward and applied against 

 the margin of the shell. Swimming auteunas reacliing the middle of the shell, their 



