Marsh—North American Species of Diaptomus. 477 
timate segment. On the outer surface of the hook, and ex¬ 
tending down the side of the segment, is an inconspicuous hya¬ 
line lamella. 
The first basal segments of the female fifth feet are armed 
with long and stout spines. The lateral hairs of the second 
basal segments are short and weak. The exopodite consists 
of three segments; the first segment is stout, its length being 
to its breadth as four to two and one-half. The second segment 
has a small spine on its outer distal angle; the inner margin 
of the hook is concave and armed with prominent teeth. The 
third segment is distinct and bears two spines, of which the 
inner is the longer. The endopodite is one-segmented, is 
more than one-half the length of the first segment of the exo¬ 
podite, and at the tip is setose and bears two long spines and 
one small one. 
The spines of the first basal segments of the fifth feet of the 
male are acute, and rather small. The second basal segment 
is trapezoidal in its general outline, longer than broad, its dis¬ 
tal end the broader, and is distinctly convex on its inner and 
outer margins; the lateral hair is small and is near the distal 
end; on the inner margin, beyond the middle, is a hyaline 
projection with a rounded outline. The first segment of the 
exopodite is wider than long, and bears on its posterior face at 
about two-thirds of its length a transverse ridge. The second 
segment of the exopodite is a little more than twice as long as 
wide, and approximately rectangular in form; about midway 
of the posterior surface is a short, curved ridge; at the middle 
of the posterior surface, near the outer margin, is a semi-cir¬ 
cular hyaline projection; the lateral spine is near the distal 
end of the segment; the terminal hook is about as long as the 
rest of the right foot exclusive of the first basal segment, is 
slender, and bent at near its middle into very nearly a right 
angle; the denticulations of its inner margin are very fine. 
The endopodite of the right fifth foot is short and stout, barely 
exceeding one-half the length of the first segment of the exopo¬ 
dite, and is setose at the tip. 
