Marsh—North American Species of Diaptomus. 447 
produced backward, each angle bilobed, the outer lobe about 
twice as large as the inner (in the male this segment is salient). 
Abdomen peculiar in that there is a sudden narrowing at the 
beginning of the third segment. First abdominal segment of 
the female armed with a large spine on each side; second and 
third segments subequal, about twice as wide as long. Furcal 
rami subquadrate, ciliate on the inner margin. Furcal setae 
rather short, densely plumose. There is but little difference 
in the length of the abdominal segments of the male. 
“Antennae 25-segmented, reaching to the middle of the ab¬ 
domen. The right antenna of the male is greatly swollen an¬ 
terior to the geniculating joint. The antepenultimate segment 
bears a broad hook-like process, which does not reach to the end 
of the penultimate segment. 
“Second basal segment of the fifth foot of the female with the 
usual delicate hair at the outer margin. First segment of the 
exopodite short and broad. Second segment large, about one 
and one-half times as long as the first, armed on the middle 
third of the inner margin with seven or eight very large, strong, 
pointed spines, and on the outer margin and opposite the upper 
spines of the inner margin with three or four spines. Third 
segment distinct, armed with two spines, the outer one short, 
thick, sharp, smooth, the inner one about twice as long and 
armed with a few rather strong spinules. Just without these 
spines, on the second segment, is a shorter smooth spine. The 
endopodite of the fifth foot of the female is distinctly two-seg¬ 
mented, the first segment subquadrate, the second as wide as 
the first and nearly twice as long, and armed at the tip with two 
thick, heavy spines reaching to the end of the second segment of 
the exopodite. These spines are armed with heavy spinules. 
Disregarding the spines, the endopodite reaches just to the end 
of the first segment of the exopodite. 
“Second basal segment of the right fifth foot of the male sub¬ 
quadrate, about twice as long as wide; on the posterior surface 
a large, smooth, hyaline lamella occupying about a third of the 
inner margin near the middle, and near the outer distal angle 
a minute cuticular process bearing a delicate hair. First seg- 
