Marsh — North American Species of Diaptomus. 4Y9 



1897. Diaptomus sanguineus Scliacht, p. 133 ; 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 

 f ureal rami are setose on the inner margin. 



The antennae are 2 5 -segmented and somewhat longer than 

 the cephalothorax. The right antenna of the male is much 

 swollen anterior to the geniculating joint. The antepenidti- 

 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 the 



