Marsh—North American Species of Diaptomus. 461 
The antennae reach slightly beyond the end of the furca. 
The right antenna of the male is swollen anterior to the genic- 
ulating joint. The antepenultimate segment bears upon its 
distal extremity a hook-like process which is rather less than 
half the length of the penultimate segment. 
In the female fifth feet, the spines of the first basal segments 
are very pronounced. The second basal segments are armed 
with rather delicate lateral hairs. The first segment of the 
exopodite is stout. The second segment is of the usual form, 
and the hook is denticulate on its inner margin. The third 
segment is represented by two spines. The endopodite equals 
in length the first segment of the exopodite, and is armed at 
the tip with two spines and with short hairs. 
In the male fifth feet, the spines of the first basal segments 
are very pronounced. The second basal segment of the right 
foot is trapezoidal in form, and its length exceeds its average 
width by about one-half. The lateral hair is at about one- 
third of its length from the distal end. The first segment of 
the right exopodite is about as broad as long, and has its distal 
angle somewhat produced. The second segment of the exopo¬ 
dite is elongate, being more than three times the length of the 
first. The lateral spine is situated at about one-third the dis¬ 
tance from the proximal end, is hook-shaped, and is inserted at 
an angle with the plane of the segment—that is, it does not 
lie in the same plane with the flat surface of the segment. The 
terminal hook is elongate, falciform, with a regular curvature. 
The endopodite is short, rather less in length than the first seg¬ 
ment of the exopodite, and is of a somewhat triangular form. 
The second basal segment of the left foot is similar in form 
to the corresponding segment of the right foot, and is about 
one-half as long. The lateral hair is situated well towards the 
distal end. The first segment of the exopodite about equals 
the basal segment in length, but is more slender. The second 
segment is short, armed with a terminal pad, a pad on its in¬ 
ner surface, and with two blunt spines near the distal end. 
The pads are armed with short, stiff hairs. The endopodite 
is very slender and very nearly equals in length the two seg¬ 
ments of the exopodite. 
