542 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



16. Urosome of female 4-segmented, of male 5-segmented; rami of 



fifth legs 3-segmented, both sexes, except right exopod of 

 male, which is short and 2-segmented; fresh water (North 



America) cf? Osphranticum Forbes, 1882 



Urosome of female 3-segmented, of male 5-segmented; fifth 

 legs not as above 17 



17. Fifth thoracic segment in female with 1 pair of asymmet- 



rical posterior processes; fifth legs of male subequal in 



length 18 



Fifth thoracic segment in female with 2 pairs of symmetrical 



posterior processes; fifth legs of male very unequal in length 21 



Fifth segment in female symmetrical, without processes; rami 

 of fifth legs in female 3-segmented; in male right leg rami 

 3-segmented, left exopod 2-segmented, endopod 1-seg- 

 mented; fresh water cf 9 Hemiboeckella Sars, 1912 



18. Fifth thoracic segment in female fused with fourth; right 



fifth endopod of male well developed and distinctly seg- 

 mented 19 



Fifth thoracic segment in female distinctly separated from 

 fourth; right fifth endopod of male rudimentary, not seg- 

 mented 20 



19. Posterior processes of fifth segment in female simple, not 



reaching center of genital segment; right fifth leg of male 



longer than left; freshwater (Brazil) cT ? Boeckellina Mrdzek, 1901 '' 



Posterior processes of fifth segment in female reaching base of 

 abdomen, left one bifurcate; left fifth leg of male longer than 

 right; fresh water (Argentina) cf ? Boeckellopsis Mrdzek, 1901'^ 



20. End segment of fifth exopod in female with 4 inner setae; spine 



of second segment longer than segment; end claw of right 

 fifth exopod in male segmented; fresh water (Patagonia). 



cf 9 Paraboeckella Mrd,zek, 1901 " 

 End segment of fifth exopod in female without inner setae; 

 spine of second segment shorter than segment; end claw of 

 right exopod in male not segmented; fresh water (Brazil). 



cf 9 Pseudoboeckella Mriizek, 1901 " 



21. Inner spine of second segment of female fifth exopod twice as 



long as end segment; fifth endopods in male 3-segmented, 

 armed with many plumose setae; fresh water (Patagonia). 



cf 9 Parabroteas Mr^zek, 1901 

 Inner spine of second segment of female fifth exopod not longer 

 than end segment; fifth endopods in male rudimentary, 

 1-segmented, without setae; fresh water (Australia). 



cf 9 Boeckella Guerne and Richard, 1889 



22. First exopods 2- or 3-segmented; forehead with 2 conical proc- 



esses; setae of both maxillae and maxillipeds densely plu- 

 mose and stout; open ocean plankton 9 Bathycalanus G. O. Sars, 1905 



First exopods always 3-segmented; forehead with 1 process 

 only; setae of maxillae densely, of maxillipeds sparsely, 

 plumose and slender 23 



First exopods always 3-segmented; forehead without a process; 

 setae of both maxillae and maxillipeds sparsely plumose 

 and slender 24 



" Of doubtful validity; if valid distinguished by characters here given. 



