COPEPODS OP THE WOODS HOLE REGION 551 



94. Upper surface of fifth legs covered with small spinules; end 



segment rounded and armed with 4 spines, 2 apical, 1 inner 



and 1 outer; open ocean $ Brachycalanus Farran, 1905 (p. 75) 



Upper surface of fifth legs smooth, without spinules; end 

 segment conically pointed and wholly without spines, apical 

 or lateral; open ocean 9 Heteramalla G. O. Sars, 1907 



95. Rami of second antennae about equal in length; end segment of 



fifth legs with 3 denticulate setae; first antennae reaching the 



caudal rami; open ocean 9 Lophothrix Giesbrecht, 1895 



Endopod of second antennae much longer and stouter than 

 exopod; end segment of fifth legs with 2 slender smooth setae, 

 the inner the longer; Antarctic plankton. 9 Drepanopsis Wolfenden, 1911 



Exopod of second antenna a third to a half longer than endopod 96 



96. Fourth and fifth segments separated, fifth without processes; 



end segment of fifth legs with 3 spines; exopod of second 



antenna with 7 segments; littoral 9 Pseudotharybis T. Scott, 1909 



Fourth and fifth segments fused, with acute posterior pro- 

 cesses; end segment of fifth legs with a long curved spine and 

 a short tooth; open ocean 9 Scottocalanus G. O. Sars, 1905 (p. 80) 



Fourth and fifth segments fused but without posterior processes 97 



97. End segment of fifth leg with tiny spine on outer margin, longer 



one at apex and still longer one on inner margin, curved and 



toothed; open ocean 9 Scolecithricella G. O. Sars, 1902 (p. 83) 



End segment of fifth leg with spine and prong at apex and a 

 spine on either margin, all 3 equal in length and none of them 

 denticulate (Gulf of Gascogne) 9 Neoscolecithrix Canu, 1896 



98. Head distinctly separated from first segment; posterior corners 



of fifth segment acute; end segment of fifth legs laminate, 



4 setae (Mediterranean) 9 Xanthocalanus Giesbrecht, 1892 (p. 68) 



Head completely fused with the first segment 99 



99. End segment of fifth legs digitiform and unarmed; basal 



segment thick, with densely crowded slender spines at inner 



distal corner (Norwegian coast) 9 Pseudophaenna G. O. Sars, 1902 



End segment of fifth legs invaginated on inner margin, with 

 long inner and short apical spine; posterior corners of fifth 

 segment pointed; Antarctic plankton ._ 9 Racovitzanus Giesbrecht, 1902 



End segment of fifth legs neither digitiform nor invaginated, 



with 1 outer, 1 apical and 1 long denticulate inner spine 100 



100. Rostrum divided to its base, sinus slitlike; rostral rami passing 



insensibly into filaments; fifth leg spine twice as long as end 



segment; open ocean 9 Scaphocalanus G. O. Sars, 1900 (p. 76) 



Rostrum divided to its base, sinus broad; rostral rami passing 

 abruptly into filaments; fifth leg spine shorter than the 

 terminal segment; pelagic plankton 9 Amallothrix Sars, 1925 



Rostrum with shallow triangular sinus, its rami abruptly 

 narrowed into filaments; fifth leg spine long as end segment; 

 pelagic, at surface 9 Scolecithricella G. O. Sars, 1902 (p. 83) 



101. Forehead with single circular organ; 1 seta of left caudal ramus 



thickened and lengthened; fifth leg with 2 unequal stout 



apical spines; open ocean 9 Macandrewella A. Scott, 1909 



No organ on forehead; no thickened seta on either ramus; 

 fifth leg with 1 tiny terminal and a long slender inner spine, 

 both smooth; pelagic, at surface. 



9 Scolecithricella G. 0. Sars, 1902 (p. 83) 



