COPEPODS OF THE WOODS HOLE REGION 543 



23. Fifth legs biramose in both sexes, rami 3-segmented; posterior 



corners of metasome smoothly rounded or slightly angular; 

 urosome symmetrical; open-ocean plankton. 



c?" 9 Megacalanus Wolfenden, 1904 (p. 26) 

 Fifth legs uniramose in both sexes, female 4-segmented, male 

 3-segmented; metasome with pointed posterior corners; 

 urosome very asymmetrical; Antarctic plankton. 



cf 9 Gaussia Wolfenden, 1905 



24. First antennae do not reach posterior margin of head 25 



First antennae reach third thoracic segment; rami of second 



antennae equal; fifth legs biramose, rami 3-segmented; body 

 and appendages covered with hair; open-ocean plankton. 



9 Oentraugaptilus G. O. Sars, 1920 

 First antennae reach the abdomen and often extend some dis- 

 tance beyond tips of caudal rami 27 



25. Fifth legs uniramose in both sexes, 3-segmented in female, 5-seg- 



mented in male; right fifth leg of male with stout end claw, 

 left leg with spatula; surface (North Atlantic). 



cf 9 Paramisophria T. Scott, 1897 

 Fifth legs biramose in both sexes 26 



26. Rami of fifth legs 3-segmented in female, 1- or 2-segmented in 



male; exopod of second antenna 3-segmented, distal endopod 

 segment at right angles to basal; littoral. 



cf 9 Pseudocyclops Brady, 1872 

 Exopods of fifth legs 2-segmented, endopods 1-segmented, spine- 

 like; exopod of second antenna 6-segmented, the two endopod 

 segments in line with each other; littoral (Bahama Islands). 



9 Bhapidophorus Edwards, 1891 



27. Left, and sometimes the right, caudal ramus with one seta much 



thicker than the others and greatly elongated 28 



Setae of caudal rami neither enlarged nor greatly lengthened 35 



28. Exopod of second antenna much longer than endopod; urosome 



4-segmented; fifth legs biramose, rami 3-segmented; maxil- 

 lary palp with many lobes; open-ocean plankton. 



9 Pontoptilus G. 0. Sars, 1905 



Rami of second antennae about the same length 29 



Endopod of second antenna much longer than exopod; fifth legs 



biramose, rami 3-segmented 32 



29. Middle segment of fifth exopod in female with smooth inner 



spine; second basipod of right fifth leg in male with sausage- 

 shaped process 30 



Middle segment of fifth exopod in female with denticulated 

 inner seta; second basipod of right fifth leg in male without 

 process 31 



30. All the setae of second maxillae transformed into stout, curved 



spines; first antennae as long as entire body, or even longer; 



pelagic cf 9 Heterorhabdus Giesbrecht, 1898 (p. 131) 



Only the two end setae of second maxillae transformed into 

 curved spines; first antennae scarcely reaching behind meta- 

 some; pelagic. -,,-,,..„,,, ^,, _„ ^_ _ cf 9 Macrorhabdus G. O. Sars, 1920 



