Marsh—North American Species of Diaptomus. 451 
dopodite of the female fifth foot. It resembles D. stagnalis 
in the antennal armature and in the general form of the male 
fifth feet; hut it differs in the male fifth feet, in the form of 
the second segment of the exopodite, and in the form and size 
of the endopodite. It differs in the female fifth feet in the 
fact that the terminal spines are shorter, and that the third 
segment is not distinct. 
diaptomus clavipes Schacht. 
Plate XX, fig. 9. Plate XXI, figs. 1, 5, 6. 
1897. Diaptomus clavipes Schacht, p. 178; pi. XXXIV, figs. 
1-3; pi. XXXV, figs. 1, 2. 
1898. Diaptomus nebraskensis Brewer, p. 123; pi. VII, figs. 
1-4. 
1902. Diaptomus clavipes Beardsley, p. 45. 
1905. Diaptomus clavipes Pearse, p. 147; pi. XIII, fig. 6. 
A large species. The first segment of the cephalothorax is 
equal in length to the three following. The last segment of 
the cephalothorax is armed with two small lateral spines. 
The first segment of the female abdomen is longer than the 
rest of the abdomen. It is much dilated in front and some¬ 
what laterally. The lateral dilatations are not abrupt as in 
many species. There are two small lateral spines. The third 
segment is very short. The furca is about equal in length to 
the two preceding segments. The furcal rami are ciliate on 
the inner margin. 
The antennae are. 25-segmented, barely reaching the end of 
the furca. The right antenna of the male is much swollen an¬ 
terior to the geniculating joint; the antepenultimate segment 
is armed with a lateral hyaline lamella. 
The spines of the first basal segments of the female fifth feet 
are rather small and blunt. The lateral hairs of the second 
basal segments are of moderate length. The length of the 
first segment of the exopodite is less than twice its width. The 
second segment is stout, and the hook is almost straight. It 
