Marsh—North American Species of Diaptomus. 479 
1897. Diaptomus sanguineus Schacht, p. 183; pis. XXIII, 
XXIV, XXV. 
1898. Diaptomus sanguineus Brewer, p. 124. 
1905. Diaptomus sanguineus Pearse, p. 147. 
Rather large. The first segment of the cephalothorax is 
nearly equal in length to the rest of the cephalothorax. The 
last segment of the cephalothorax is produced laterally, and 
armed on each side with two rather prominent spines. The 
fifth cephalothoracic segment of the female has a pronounced 
dorsal hump. 
The first abdominal segment of the female equals the rest 
of the abdomen including the furca. It is expanded laterally 
and in front, and bears two pronounced lateral spines. The 
second segment is about one-half as long as the third. The 
furcal rami are setose on the inner margin. 
The antennae are 25-segmented and somewhat longer than 
the cephalothorax. The right antenna of the male is much 
swollen anterior to the geniculating joint. The antepenulti¬ 
mate segment bears at its distal end a short, stout, recurved 
hook, which is continuous with a lateral hyaline lamella of the 
segment. 
The female fifth feet are rather stout. The spines of the 
first basal segments are of moderate size. The lateral hairs 
of the second basal segments are commonly long, reaching 
nearly to the end of the first segment of the exopodite. The 
first segment of the exopodite is twice as long as broad. The 
second segment is produced into the customary hook, which is 
dentate on the inner margin. The third segment is repre¬ 
sented by two spines, of which the outer is the shorter. The 
endopodite is slender, variable in length, but commonly much 
shorter than the first segment of the exopodite. It is setose 
at tip, and armed with two rather long spines. 
In the male fifth feet, the spines of the first basal segments 
are rather small. The second basal segment of the right foot 
is trapezoidal in form, wider at the distal end. Its length is 
about twice its average width. The outer distal angle is pro¬ 
longed into a blunt or acute spine; the lateral hair is near th© 
