North American Species of Diaptomus. 123 



small cuticular projection bearing a delicate hair. First seg- 

 ment of the outer ramus subquadrate, slightly longer than 

 broad, the inner distal angle provided with a small semi- 

 elliptical hyaline lamina arising from the anterior surface of 

 the leg; second segment slightly arcuate, the two margins 

 parallel, fully twice as long as wide. Marginal spine long 

 and slender, slightly curved, about half as long as the seg- 

 ment, and inserted at the beginning of the distal third. Ter- 

 minal hook long, slender, and regularly curved ; very minutely 

 denticulate on the inner margin. 



Inner ramus of the right leg either one- or two-segmented, 

 extending beyond the end of the first segment of the outer 

 ramus ; minutely hairy at the tip. 



There is nothing distinctive about the basal segments of 

 the left leg. The first segment of the outer ramus is about 

 one and a half times as long as broad ; the inner distal angle 

 gradually rounded and minutely hairy- The second segment 

 is narrow, twice as long as broad ; armed at the tip with two 

 digitiform processes and sometimes with a much smaller 

 third process between the two. This segment appears very 

 broad and fleshy because of a cushion-like process with rugose 

 surface which extends beyond the inner margin of the seg- 

 ment for half its length. The other, upper, half is occupied 

 by a minutely hairy semicircular cushion. 



Inner ramus of the left foot either one- or two-segmented, ex- 

 tending to the middle of the last segment of the outer ramus ; 

 hairy at the tip. 



Basal segments of the fifth pair of feet in the female (PL 

 XXI., Fig. 2) not characteristic. The usual delicate hair is 

 found on the outer margin of the second basal segment. 

 First segment of outer ramus long and narrow, more than 

 twice as long as broad. Second segment almost as long as 

 the first, narrow, tapering to a fine point, delicately spinose 

 at the inner margin. Third segment wanting; represented 

 by two spines, both sharp and slender, the inner about twice 

 as long as the outer. 



Inner ramus of fifth leg of female one-segmented, project- 

 ing slightly beyond the end of the first segment of the outer 



