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 cf 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- 



