Marsh—North American Species of Diaptomus . 427 
anterior part, and is armed with two very minute spines. The 
second segment is much shorter than the third, and the two are 
sometimes only indistinctly separated. The furcal rami are 
about equal in length to the third segment; they are twice as 
long as broad. The setae are unusually long. 
The antennae are 25-segmented, and reach beyond the end of 
the furca. The right antenna of the male is swollen anterior 
to the geniculating joint, but not markedly so; the antepenul¬ 
timate segment bears a long, slender process, slightly curved at 
the end, which reaches, sometimes, almost to the end of the last 
segment. The setae of the swimming feet are unusually long. 
The spines of the first basal segments of the female fifth feet 
are rather small. The lateral hair of the second basal segment 
is of moderate length. The first segment of the exopodite is 
slender, its length being considerably more than twice its width. 
The hook of the second segment is only slightly curved, and is 
finely denticulate on the inner margin. There is a short spine 
on the outer distal angle. The third segment is rudimentary, 
not completely separated from the second. It is armed with two 
spines, of which the inner is the longer. The endopodite is 
acuminate, very small and rudimentary. 
The spines of the first basal segments of the male fifth feet 
are small. The second basal segment of the right foot is quad¬ 
rate, longer than broad. The lateral hair is situated at the be¬ 
ginning of the distal third. The first segment of the right ex¬ 
opodite is of the same form and size as the second basal seg¬ 
ment. The second segment is twice as long as the first. The 
lateral spine is small and situated proximad of the middle. The 
terminal hook is short, thick, symmetrically curved, and slightly 
denticulate on the inner margin. Its length is somewhat less 
than that of the rest of the exopodite. The endopodite is very 
small and rudimentary. The second basal segment of the left 
foot is quadrate, and much wider than long. The lateral hair 
is situated well towards the distal end. The first segment of 
the exopodite is longer than wide, its inner and outer margins 
are convex, and its distal end is only about one-half as wide as 
the proximal. It is setose on its inner margin. The second 
