North American Species of Diaptomus. 113 



37 (38). Inner ramus of right leg rudimentary, extending but 



slightly beyond the end of the segment to which it is 

 attached. Marginal spine below middle of segment, 

 slender, fully half as long as the very long segment. 

 Terminal hook shorter than the preceding segment. 

 Left leg (disregarding terminal spines) not reaching end 

 of first segment of outer ramus of right leg. Last seg- 

 ment with two spines : one long, slender, outcurved ; the 

 other short, stout. Inner ramus extending almost to 

 end of last segment of outer ramus. lintoni. 



38 (37). Inner ramus of right leg not rudimentary, extend- 



ing to middle of first segment of outer ramus or beyond. 



39 (40), Inner ramus of right leg extending about to middle 



of first segment of outer ramus. Marginal spine below 

 middle, about half as long as segment. Terminal 

 hook longer than the preceding segment. Second basal 

 segmen^ with hyaline lamina on inner margin. Left 

 leg (disregarding terminal spines) reaching about to 

 middle of first segment of outer ramus of right leg ; 

 inner ramus reaching end of first segment of outer 

 ramus, corrugate on inner margin. stagnalis. 



40 (39). Inner ramus of right leg extending beyond the end of 



the very short first segment of outer ramus. Marginal 

 spine below middle of segment, stout, longer than 

 segment. Terminal hook very long, stout, longer than 

 remainder of leg. Left leg extending beyond end 

 of first segment of outer ramus of right leg ; second 

 segment with ciliate lamina on inner margin ; inner 

 ramus reaching end of first segment of outer ramus. 



albuquerquensis. 



41 (34). Process curved. 



42 (43). Process small, not reaching middle of penultimate 



article. Marginal spine below middle ; rather stout, 

 less than a third the length of segment, Terminal hook 

 noticeably longer than the two preceding segments. 

 First segment of outer ramus with hyaline lamina on 

 inner margin, the inner apical angle of which is not 



