554 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



121. Fifth legs 3-segmented, apical segments denticulate, left leg 



longer than right; urosome segments fringed posteriorly 



with spines; littoral, marine 9 Parastephos G. O. Sars, 1902 



Left fifth leg 2- to 4-seginented, right leg lacking; urosome 

 segments not fringed with posterior spines; outer caudal 

 setae lacking; tropical, marine ? Ctenocalanus Giesbrecht, 1888 



122. Exopod of second antenna 7-segmented; right fifth leg 4-seg- 



mented 123 



Exopod of second antenna 6-segmented; right fifth leg 3- or 



5- segmented 124 



123. Left fifth leg 6-segmented; tip of right leg reaching third 



segment of left leg; posterior corners of metasome sharply- 

 pointed; littoral, marine cT Undinopsis G. O. Sars, 1884 



Left fifth leg 5-segmented; tip of right leg reaching fourth 

 segment of left leg; posterior corners of metasome evenly 

 rounded; open ocean cf Pseudocalanus Boeck, 1872 (p. 43) 



124. Right fifth leg 3-segmented, its tip reaching third segment of 



left leg; the latter 6-segmented; endopod of second an- 

 tenna with 15 end setae; Uttoral, marine. 



cf Microcalanus G. O. Sars, 1901 

 Right fifth leg 5-segmented, its tip reaching fifth segment of 

 left leg; the latter 6-segmented; endopod of second antenna 

 with only 8 setae; bottom, littoral- cf Pseudophaenna G. O. Sars, 1902 



125. Left fifth leg swollen, right slender, with or without a claw 126 



Basipod only of left leg swollen, but both legs misshapen 127 



126. Right fifth leg 4-segmented, without a claw; left leg 5-seg- 



mented, apical appendages leaf-like; third segment the 

 largest, without a lamella; bottom plankton, cf Stephos T. Scott, 1892 

 Right fifth leg 4-segmented, with denticulated claw; left leg 

 5-segmented, no leaf -like appendages; second segment the 

 largest, with a lamella; bottom plankton. 



cf Parastephos G. O. Sars, 1902 



127. Swollen basipod with pectinated row of spines; right leg 



2-segmented, left 4-segmented, its second segment with 



irregular processes; bottom plankton cf Diaixis G. O. Sars, 1902 



Swollen basipod without spines; right leg 4-segmented, left 

 5-segmented, no processes on second segment; left end 

 segment small and cochlear; littoraL. cf Pseudocyclopia T. Scott, 1892 



128. Right fifth leg uniramose, 3-segmented, left biramose, exopod 



3-segmented, endopod 1-segmented; fifth legs reaching 



beyond tips of caudal rami; littoral cf Tharybis G. O. Sars, 1902 



Both fifth legs biramose, exopods 3-segmented, endopods 

 1-segmented, rudimentary; right leg longer than left and 

 ending in a claw; bottom plankton cT Undinopsis G. O. Sars, 1884 



Both fifth legs biramose, asymmetrical, not segmented as 



above 129 



