North American Species of Diaptomus. 147 



Antennae of the female 2 5 -segmented, extending well be- 

 yond the tips of the furcal setae ; somewhat shorter in the 

 male, reaching about to the tips of the furcal setae. Eight 

 male antenna moderately swollen beyond the thirteenth seg- 

 ment. Beyond the twelfth segment the antenna is armed as 

 follows: 13, with large process; 14, process, short seta, and 

 very long seta; 15, very short stunted spine, short seta, and 

 long seta; 16, a short and a long seta; 17, process, short 

 seta, and long seta ; 18, large process ; 19 and 20 (completely 

 ankylosed), short stunted spine and long seta; 20, 21, and 

 22 (also completely ankylosed), two setae, and a hooked 

 process extending beyond the middle of the penultimate 

 article; 24, two seta?; and 25, four setae. 



Left fifth leg of the male (PL XXVII. , Fig. 4) short, not 

 reaching to the end of the second segment of the outer ramus 

 of the right leg. First and second basal segments subequal, 

 the first armed at the middle of the outer margin with a 

 rather long sharp spine ; the second slightly broader than 

 the first, and provided a short distance above the outer distal 

 angle with the usual delicate hair, and at the middle of the 

 inner margin with a small hyaline plate. First segment of 

 the outer ramus about twice as long as wide ; outer margin 

 arcuate, inner margin convex and delicately hairy. Second 

 segment racket-shaped, the broad basal half being almost 

 circular ; hairy on the inner margin. The digitiform termi- 

 nal half is blunt and delicately denticulate on the margin. 

 From the anterior aspect projects a delicately hairy spine 

 about as long as the digitiform process, but more acute and 

 pointing inward. 



Inner ramus of left fifth leg short, one-segmented, barely 

 reaching to the end of the first segment of the outer ramus ; 

 margins slightly sinuous ; apex bluntly rounded, very deli- 

 cately hairy, the hairs at the apical angles being somewhat 

 stouter and spine-like. 



First basal segment of right fifth leg of male subquadrate, 

 slightly longer than broad ; armed at the outer distal angle 

 with a stout, sharp spine pointing straight outward. Second 

 basal segment subquadrate, about equal to the first, and 



