Marsh—North American Species of Diaptomus. 419 
to their breadth as one and one-lialf to one; they are ciliate on 
both inner and outer margins. 
The first pair of antennae in the female are 25-segmented, 
and reach about to the furca. The antepenultimate segment 
of the right antenna of the male bears an unguiform process, 
slightly longer than the penultimate segment. 
In the female fifth foot, the exopodite is three-segmented. 
The first segment is somewhat elongate, its length being nearly 
three times its width. The second segment is prolonged into 
the customary hook. The hook is arcuate, denticulate on the 
inner margin, the last tooth being the largest. The segment 
bears a small spine at its outer distal angle. The third seg¬ 
ment is small but distinct, and bears two small spines. The 
endopodite is one-segmented, about equal in length to the first 
segment of the exopodite, and bears at the tip two unusually 
long spines which.are ciliate at base. 
In the male, the second basal segment of the right foot is 
quadrate, longer than wide, and bears the lateral seta a little 
beyond the middle. The first segment of the exopodite is 
quadrate and short, being only about one-half the length of the 
second basal segment. The second segment is rectangular, 
rather less than twice the length of the first; the lateral spine 
is situated at the distal angle, and about midway of the inner 
margin there is a minute spine. The terminal hook is long, 
equaling the whole right foot exclusive of the first basal seg¬ 
ment, is sigmoid, and slender towards the apex. The endo¬ 
podite is small, barely reaching the middle of the second seg¬ 
ment of the exopodite, is imperfectly two-segmented or one- 
segmented, and bears a spine at the apex. 
The left fifth foot of the male reaches about to the middle 
of the second segment of the exopodite of the right foot. The 
second basal segment is longer than broad, shorter than the cor¬ 
responding segment of the right foot, is concave on the outer 
margin and convex on the inner; the lateral hair is situated 
at about three-fourths of its length. The first segment of the 
exopodite is twice as long as wide, nearly as long as the second 
basal segment. The second segment is about equal in length 
