546 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



49. Right antenna modified for preiiension 50 



Left antenna modified for prehension 52 



50. Both rami of fifth legs 3-segmented, endopods subsymmetrical, 



exopods asymmetrical; exopod of second antenna 8-segmented, 

 shorter than endopod; open ocean, cf Augaptilus Giesbrecht, 1889 (p. 135) 

 Rami of fifth legs not segmented alike 51 



51. Exopods of fifth legs 2-segmented, right endopod lacking, left 



endopod laminate, 1-segmented; exopod of second antenna 

 5-segmented, basal segment long; littoral, among algae. 



c? Isias Boeck, 1865 

 Left 5th exopod 2-segmented, right 3-segmented; endopods 

 symmetrical, 3-segmented; exopod of second antenna 6- 

 segmented, its basal segment exceptionally short; pelagic, at 

 surface cf Centropages Kr0yer, 1849 (p. 85) 



52. Fifth legs subsymmetrical, rami 3-segmented with plumose setae 53 



Fifth legs decidedly asymmetrical, often without plumose setae 55 



53. Endopod of second antenna three or four times as long as 



exopod, latter 7-segmented; middle segment of right fifth 



exopod with smooth inner margin; pelagic, cf Haloptilus Giesbrecht, 1898 

 Rami of second antennae subequal, or endopod the longer; 



exopod 8-segmented; middle segment of right fifth exopod 



with a strong grasping process; open ocean. 



c?" Augaptilus Giesbrecht, 1889 (p. 135) 

 Exopod of second antenna much longer than endopod 54 



54. Middle segment of right fifth exopod with small inner spine; 



end section of left antenna 4-segmented, first segment twice 

 as long as second segment; open ocean. _ cf Pontoptilus G. O. Sars, 1905 < 

 Middle segment of right fifth exopod with smooth inner margin; 

 end section of left antenna 5-segmented, first segment 

 scarcely longer than second; open ocean, c? Heteroptilus G. O. Sars, 1920 



55. Exopods of fifth legs 3-segmented, endopods 1-segmented; 



posterior corners of metasome sharply pointed; forehead 



with wedge-shaped process; open ocean. cT Arietellus Giesbrecht, 1892 



Both rami of fifth legs 3-segmented; posterior corners of meta- 

 some smoothly rounded; forehead smooth, without a wedge- 

 shaped process; open-ocean plankton cT Euaugaptilus Sars, 1920 



Exopods of one or both fifth legs 2-segmented, endopods 1-, 2-, 



or 3-segmented 56 



56. Basipods, exopods, and endopods of fifth legs each 2-segmented 



but asymmetrical; end segments of exopods broad lamelliform, 



with narrow tips; open ocean cf Paraugaptilus Wolfenden, 1904 



Basipods, exopods, and endopods of fifth legs not segmented alike 57 



57. Rami of left fifth leg 3-segmented, of right leg 2-segmented; 



distal segment of right exopod shutting down against the 

 proximal, forming a chela; open ocean. 



c^ Lucicutia Giesbrecht, 1898 (p. 128) 

 Exopods of fifth legs 3-segmented; right endopod lacking, left 

 endopod 1-segmented, unarmed; right exopod not operating 

 to form a chela; open ocean <f Phyllopus Brady, 1883 (p. 136) 



