540 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



KEY TO THE GENERA OF THE SUBORDER CALANOIDA 



(The swimming legs, especially the fifth pair, and the second antennae furnish the 

 best distinctive characters in this group.) 



1. Endopods of third and fourth swimming legs 3-segmented (see 85) 2 



Endopods of third and fourth swimming legs 2-segmented 157 



Endopods of third and fourth swimming legs 1-segmented 177 



Endopods of third legs 2-segmented, of fourth legs 3-segmented, 



exopods 3-segmented; first exopods 2-segmented, endopods 1- 

 segmented; fifth legs uniramose, 3-segmented, no setae; 



bottom (Gulf of Guinea) cf ? Heteramalla G. O. Sars, 1907 



Endopods of third legs 2-segmented, of fourth legs 1-segmented, 

 exopods 2-segmented; rami of first legs 3-segmented; fifth legs 

 biramose, rami 1-segmented, armed with spines; surface 

 (south Pacific) cf 9 Guernella Schmeil, 1897 



2. Endopods of first swimming legs 3-segmented 3 



Endopods of first swimming legs 2-segmented 58 



Endopods of first swimming legs 1-segmented 76 



3. A circular brown spot (light organ) on right or left side of first 



segment; fifth legs uniramose, 2- to 4-segmented in female, 5- 

 segmented in male, asymmetrical; pelagic. 



d' 9 Pleuromamma Giesbrecht, 1898 (p. 123) 

 No circular brown spot on either side of first segment 4 



4. Basal segment of second endopod deeply invaginated, with spines 



on sides of invagination; fifth legs uniramose, 3- or 4-seg- 

 mented in female, 5-segmented in male; pelagic, to 2,000 



fathoms cf 9 Metridia Boeck, 1865 (p. 117) 



No invagination and no spines on basal segment of second endopod 5 



5. Terminal exopod segment of third and fourth legs with 1 lateral 



spine, 1 at the distal corner, and 1 terminal 6 



Terminal exopod segment of third and fourth legs with 2 lateral 



spines, 1 at the distal corner, and 1 terminal 22 



6. Second basipod of first legs with a curved spine; no marginal 



teeth on third and fourth exopods in female; left fifth exopod 



in male without setae; pelagic (North Atlantic). 



d^ 9 Neocalanus G. O. Sars, 1925 (p. 27) 

 First legs without basipod spine; outer margins of third and 



fourth exopods toothed; fifth legs biramose, rami 3-segmented; 



first antennae asymmetrical; littoral 9 Metranura Brady, 1915 



First legs without basipod spine; no marginal teeth on third and 



fourth exopods; first antennae symmetrical 7 



7. Urosome distorted; caudal rami asymmetrical; fifth legs of male 



uniramose, the right leg 5-segmented and chelate, the left leg 



2-segmented and short; littoral cflsocope Brady, 1915 



Urosome and caudal rami symmetrical; male fifth legs not as 



above 8 



8. Terminal spines of third and fourth exopods with both margins 



smooth . 9 



Terminal spines of third and fourth exopods with one or both 



margins pectinate, denticulate, or setaceous 12 



