North American Species of Diaptomus. Ill 



23 (24). Inner ramus of right leg rudimentary, barely sur- 



passing end of segment from which it arises. Mar- 

 ginal spine about at middle of segment, very small. 

 Terminal hook shorter than the very long preceding 

 segment. Left leg extending slightly beyond end of 

 first segment of outer ramus of right leg ; inner ramus 

 very narrow, extending about to middle of second seg- 

 ment of outer ramus. minutus. 



24 (23). Inner ramus of right leg not rudimentary, longer 



than first segment of outer ramus. 



25 (26). Marginal spine well above middle of segment, about 



half as long as segment. Terminal hook longer than the 

 two preceding segments. Inner ramus of right leg very 

 narrow. Left leg reaching slightly beyond end of first 

 segment of outer ramus of right leg ; inner ramus extend- 

 ing to middle of last segment of outer ramus, ashlandi. 



26 (25). Marginal spine below middle of segment, less than 



half as long as segment. Terminal hook very slender, 

 longer than the two preceding segments. First seg- 

 ment of outer ramus with hyaline lamina at inner distal 

 angle. Left leg extending about to middle of second 

 segment of outer ramus of right leg ; inner ramus ex- 

 tending barely to middle of second segment of outer 

 ramus. sicilis. 



27 (16). Process shorter than penultimate article. 



28 (33). Process the continuation of a hyaline lamina. 



29 (30). Process extending at least to middle of penultimate 



article. Hyaline lamina extending but little more than 

 the distal half of the segment. Marginal spine below 

 middle of segment ; shorter than segment. Terminal 

 hook longer than the two preceding segments but not 

 as long as those and the second basal segment together. 

 Inner ramus of right leg extending slightly beyond end 

 of first segment of outer ramus. Left leg extending 

 slightly beyond end of first segment of outer ramus of 

 right leg ; inner ramus extending about to middle of 

 last segment of outer ramus. novamexicanus. 



