COPEPODS OF THE WOODS HOLE REGION 553 



112. Head fused with first thoracic segment; urosome as wide as 



raetasome, one-fourth as long; no spines on the posterior 

 surface of fourth basipod; pelagic, near surface. 



9 Scolecithrix Brady, 1883 (p. 81) 

 Head distinctly separated from first thoracic segment; urosome 



much narrower as well as shorter than the metasome 113 



113. Metasome twice as long and three times as wide as urosome; 



first basipod of fourth legs with many spines on posterior 

 surface; tropical marine plankton. ? Euchirella Giesbrecht, 1888 (p. 55) 

 Metasome four times as long and five times as wide as urosome; 

 posterior surface of fourth basipod smooth, without spines; 

 tropical marine plankton 9 Phaenna Glaus, 1863 



114. Basipod and exopod of second and third legs wider than in 



fourth legs; fifth legs uniramose, in female 3-segmented, in 

 male left 5-segmented, right 1-to 3-segmented; open ocean. 



cT 9 Clausocalanus Giesbrecht, 1888 (p. 42) 

 Basipod and exopod of second and third legs like those of 



fourth legs 115 



115. Fifth legs uniramose and symmetrical, females only 116 



Fifth legs uniramose and asymmetrical, both sexes 120 



One or both fifth legs biramose, males only 128 



Fifth legs wholly lacking, females only 131 



116. First antennae reaching at least to the genital segment; exo- 



pod of second antennae 6-segmented 117 



First antennae not reaching beyond posterior margin of head; 



exopod of second antennae usually 7-segmented 119 



117. Head with dorsal carina and frontal crest; rami of second 



antennae subequal; fourth and fifth body segments fused 

 with sharp posterior corners; polar plankton. 



9 Amallophora T. Scott, 1894 

 Neither carina nor crest; rami of second antennae subequal; 

 fourth and fifth segments separated, fifth with 2 spines on 

 each corner; fifth legs 3-segmented; bottom, littoral. 



9 Oothrix Farran, 1905 

 Neither carina nor crest; exopod of second antenna twice as 



long as the endopod 118 



118. End segment of fifth legs digitiform, not so long as the 2 prox- 



imal segments combined; fifth metasome segment with 

 pointed corners; bottom, littoral- _ 9 Pseudophaenna G. O. Sars, 1902 

 End segment of fifth legs laminate, twice as long as 2 proximal 

 segments combined; fourth and fifth segments fused with 

 rounded posterior corners; littoral, marine. 9 Tharybis G. O. Sars, 1902 



119. Basal segments of fifth legs each with inner spine; exopod of 



second antenna 6-segmented, shorter than endopod; fifth 

 segment with rounded corners; littoral, marine. 



9 Pseudocyclopia T. Scott, 1892 

 No iimer spines on fifth basipods; exopod of second antenna 

 7-segmented, longer than endopod; fifth segment with 

 pointed posterior corners (Scottish seas). 



9 Pseudotharybis T. Scott, 1909 



120. Females, fifth legs asymmetrical in segments, or length, or both 121 



Males, fifth legs asymmetrical, but not swollen or misshapen 122 



Males, fifth legs conspicuously swollen and misshapen 125 



