548 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



66. First antennae of female 25-segmented; urosome 3-segmented; 



right fifth exopod of male 2-segmented, endopod 1- or 2-seg- 

 mented; rami of left leg 2- or 1-segmented; fresh water. 



cf ? Diaptomus Westwood, 1836 (p. 90) 

 First antennae of female 26-segmented; urosome 2-segmented; 



fifth legs of male not segmented as above 67 



67. Right fifth exopod of male 2-segmented, with smooth end claw, 



endopod 3-segmented; left exopod 1-segmented, fused with 

 basipod, endopod lacking; fresh water (Transvaal). 



d^ 9 Adiaptomus Cooper, 1906 

 Right fifth exopod of male 3-segmented, with serrated end claw, 

 endopod 2-segmented; left exopod 2-segmented, separated 

 from basipod; endopod lacking; fresh water (Transvaal). 



cf 9 Metadiaptomus Methuen, 1910 



68. Outer margin of second, third, and fourth exopods not toothed; 



fifth legs uniramose, 3-or4-segmented in female; in male right 

 leg 4-segmeated, left leg 5-segmented; tropical oceans. 



& ? Calocalanus Giesbrecht, 1888 (p. 39) 

 Outer margin of second, third, and fourth exopods toothed 69 



69. Fifth legs lacking in female or reduced to knobs; left leg only- 



present in male; exopod of second antenna as long as endoped, 



7-segmented; marine plankton cf 9 Acrocalanus Giesbrecht, 1888 



Both fifth legs present in male and female 70 



70. Fifth legs uniramose, each 2-segmented in female; in male right 



leg 2-segmented, left 5-segmented; exopod of second antenna 

 shorter than endopod, 7-segmented; marine plankton. 



cT 9 Paracalanus Boeck, 1865 (p. 37) 

 Fifth legs uniramose in male, right leg 2-segmented, left leg 

 6-segmented; exopod of second antenna longer than endopod, 

 but only 2-segmented; brackish water-- cf Piezocalanus Grandori, 1912 



71. Exopod of first legs 3-segmented; fifth legs lacking in female 72 



Exopod of first legs 3-segmented; fifth legs uniramose in female, 



2-segmented; both fifth legs biramose in male, exopods 3- 

 segmented, endopods 2-segmented; polar plankton. 



cf 9 Scaphocalanus (part) G. O. Sars, 1900 (p. 76) 

 Exopod of first legs 2-segmented; fifth legs uniramose in female, 

 3-segmented; left leg biramose in male, right leg uniramose, 

 with only 1 segment; marine plankton. 



cf 9 Rhincalanus Dana, 1852 (p. 34) 



72. Endopod of second antenna longer than exopod; end spines of 



second to fourth exopods with smooth margins; fifth legs uni- 

 ramose in the male; marine plankton, cf 9 Eucalanus Dana, 1852 (p. 30) 

 Exopod of second antenna longer than endopod; end spines 

 of second to fourth exopods with 50 to 60 crowded teeth on 

 their outer margins; Antarctic plankton. 9 Faroella Wolfenden, 1904 



73. Fifth legs entirely lacking in female, biramose in male, exopods 



3-segmented, endopods 1-segmented, rudimentary; exopod 

 of second antenna 7-segmented; deep-water plankton. 



cf 9 Pseudaetideus Wolfenden, 1904 

 Fifth legs present and uniramose in both sexes 74 



