550 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



Head separated from first segment, and fourth from fifth seg- 

 ment; caudal rami without cilia on inner margin; apical spine 

 of fifth leg toothed; Antarctic plankton. 9 Isocalanus Wolfenden, 1911 



85. Fifth legs 4-segmented in both sexes; endopod of third legs 



2-segmented; fourth and fifth segments distinctly separated, 

 the fifth often with wings; fresh and brackish water. 



cf 9 Eurytemora Giesbrecht, 1881 (p. 107) 

 Fifth legs rudimentary or lacking in female, biramose in male; 

 third endopod 3-segmented; fourth and fifth segments partly 

 fused, without wings; open ocean cf 9 Monacilla G. O. Sars, 1905 



86. Posterior surface of rami of third and fourth legs armed with 



spines, often arranged in transverse rows and of large size 87 



Posterior surface of third and fourth legs smooth ; without spines 114 



87. Fifth legs uniramose and symmetrical 88 



Fifth legs uniramose and asymmetrical (see 105) 102 



Fifth legs biramose, males only 107 



Fifth legs lacking, females only 111 



88. Each fifth leg 4-segmented, end segment with 3 denticulate 



setae; first antennae nearly reaching caudal rami; head and 



first segment fused; open ocean 9 Lophothrix Giesbrecht, 1895 



Each fifth leg 3-segmented 89 



Each fifth leg 2-segmented 98 



Each fifth leg 1-segmented 101 



89. Head distinctly separated from first segment 90 



Head completely fused with the first segment 95 



90. Frons projecting hke a capuchin cowl, covering 2 light organs; 



exopod of second antenna longer than endopod and made up 



of 6 segments; open ocean 9 Cephalophanes G. O. Sars, 1907 



Neither cowl nor light organs, but a normal rostrum 91 



91. Apex of second maxilla with curved spines pectinate on their in- 



ner margins; head without frontal spine, usually without me- 

 dian crest 92 



Apex of second maxilla with 1 stout claw, having smooth mar- 

 gins; head with or without frontal spine, usually with a me- 

 dian crest 93 



Apex of second maxilla with neither claw nor pectinate spines; 



head with neither median crest nor frontal spine 94 



92. Upper surface of fifth legs with coarse hairs, inner margins 



dentate, without spines; end segment trilobate, with dentic- 

 ulate spines; open ocean 9 Xanthocalanus Giesbrecht, 1892 (p. 68) 



Upper surface of fifth legs smooth; inner margins each with 1 

 spine and a few small teeth; end segment conical, with 

 smooth spines; Antarctic plankton-. 9 Talacalanus Wolfenden, 1911 ^^ 



93. Head with or without a frontal spine; rostrum deeply bifurcate, 



with curved filaments; fifth legs with hairs on last 2 segments 



only; open ocean 9 Cornucalanus Wolfenden, 1905 (p. 74) 



Head without a frontal spine; rostrum slightly bifurcate, no fil- 

 aments; fifth legs with all 3 segments densely covered with 

 long hairs; open ocean 9 Onchocalanus G. O. Sars, 1905 



V Validity doubtfu.1, usually made a synonym, of Xanthocalanus. 



