Marsh — North American Species of Diaptomus. 477 



timate segment. On the outer surface of the hook, and ex- 

 tending down the side of the segment, is an inconspicuous hya 

 line lamella. 



The first basal segments of the female fifth feet are armed 

 with long and stout spines. The lateral hairs of the second 

 basal segments are short and weak. The exopodite consists 

 of three segments ; the first segment is stout, its length being 

 to its breadth as four to two and one-half. The second segment 

 has a small spine on its outer distal angle; the inner margin 

 of the hook is concave and armed with prominent teeth. The 

 third segment is distinct and bears two spines, of which the 

 inner is the longer. The endopodite is one-segmented, is 

 more than one-half the length of the first seg-ment of the exo- 

 podite, and at the tip is setose and bears two long spines and 

 one small one. 



The spines of the first basal segments of the fifth feet of the 

 male are acute and rather small. The second basal segment 

 is trapezoidal in its general outline, longer than broad, its dis- 

 tal end the broader, and is distinctly convex on its inner and 

 outer margins; the lateral hair is small and is near the distal 

 end; on the inner margin, beyond the middle, is a hyaline 

 projection with a rounded outline. The first segment of the 

 exopodite is wider than long, and bears on its posterior face at 

 about two-thirds of its length a transverse ridge. The second 

 segment of the exopodite is a little more than twice as long as 

 wide, and approximately rectangular in form; about midway 

 of the posterior surface is a short, cui*ved ridge ; at the middle 

 of the posterior surface, near the outer margin, is a semi-cir- 

 cular hyaline projection; the lateral spine is near the distal 

 «nd of the segment; the terminal hook is about as long as the 

 rest of the right foot exclusive of the first basal segment, is 

 slender, and bent at near its middle into very nearly a right 

 angle; the denticulations of its inner margin are very fine. 

 The endopodite of the right fifth foot is short and stout, barely 

 exceeding one-half the length of the first segment of the exopo- 

 dite, and is setose at the tip. 



