North American Species of Diaptomus. 109 



9 (8). Marginal spine of right leg below middle of segment ; 



slender, less than half as long as segment. Terminal 

 hook longer than the two preceding segments, a sharp 

 angle dividing it approximately into halves. Inner 

 ramus reaching end of first segment of outer ramus ; 

 apex bluntly rounded. Left leg reaching beyond middle 

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

 ment of outer ramus ending in a forcipate structure ; 

 outer digitiform process stout, armed on inner margin 

 near tip with cushion-like hairy process. reighardi. 



10 (4, 5). Inner ramus of right fifth foot reaching well 



beyond end of first segment of outer ramus. 



11 (12). Inner ramus of left fifth foot long, extending beyond 



middle of second segment of outer ramus ; leg itself 

 (disregarding terminal spines) not reaching end of first 

 segment of outer ramus. Marginal spine of right leg 

 inserted below middle of segment, near apical angle ; 

 much less than half as long as segment. Terminal 

 hook shorter than the preceding segment. piscine?. 



12 (11). Inner ramus of left fifth foot short, not extending 



beyond middle of second segment of outer ramus. 



13 (14). Inner ramus of left fifth foot not reaching to middle of 



second segment of outer ramus ; leg itself reaching end 

 of second segment of outer ramus of right leg. Mar- 

 ginal spine below middle of segment near apical angle ; 

 almost as long as segment. Terminal hook longer 

 than the preceding segment. Inner ramus of right 

 foot extending beyond end of first segment of outer 

 ramus. oregonensis. 



14 (13). Inner ramus of left fifth foot reaching middle of sec- 



ond segment of outer ramus ; leg itself reaching about 

 to middle of second segment of outer ramus of right leg. 

 Marginal spine below middle of segment, about half as 

 long as segment. Terminal hook longer than the two 

 preceding segments. Inner ramus of right foot ex- 

 tending to middle of second segment of outer ramus. 



mississippiensi8. 



