COPEPODA FROM IFALUK ATOLL 169 



The following keys have been adapted from Lang (1948, p. 565). 

 Key to Species of Idomene 



FEMALES 



1. Thoracic somites 2 to 4 each with 3 spinules on the epimeral plates. 



I. simulans (Brady) 

 Epimeral plates of all thoracic somites free from spinules 2 



2. Exopodite and baso-endopodite of leg 5 fused . . I. coronata (T. Scott) 

 Exopodite of leg 5 free 3 



3. Baso-endopodite of leg 5 with 6 setae I. borealis G. O. Sars 



Baso-endopodite of leg 5 with 5 setae 4 



4. Exopodite of leg 5 with 4 setae I. antarctica (Giesbrecht) 



Exopodite of leg 5 with 5 or 6 setae 5 



5. Exopodite of leg 5 with 6 setae I. pectinata (T. and A. Scott) 



Exopodite of leg 5 with 5 setae 6 



6. Baso-endopodite of leg 5 reaches halfway along exopodite 7 



Baso-endopodite of leg 5 reaches end of exopodite or beyond 12 



7. 1st segment of endopodite leg 1, 2 times as long as wide 8 



1st segment of endopodite leg 1, 2^^ times as long as wide or longer ... 11 



8. Endopodite of leg 1 distinctly 3-segmented .... I. forficata Philippi 

 Endopodite of leg 1, 2-segmented 9 



9. Terminal claws of endopodite leg 1 of unequal length. 



I. purpurocincta (Norman and T. Scott) 



Terminal claws of endopodite leg 1 of equal length though of different 



shape 10 



10. Baso-endopodite of leg 5 with 5 spiniform setae. 



I. novaezealandiae (Thomson) 

 Baso-endopodite of leg 5 with 5 flat, dagger-shaped spines. 



I. maldiviae (Sewell) 



11. 1st segment of endopodite leg 1 longer than whole exopodite. 



I. scotti Lang 

 1st segment of endopodite leg 1 shorter than whole exopodite. 



I. ferrieri (T. Scott) 



12. Antennule 6-segmented 13 



Antennule 7-segmented 14 



13. Exopodite and baso-endopodite of leg 5 with short, spiniform setae. 



I. laticaudata (Thompson and A. Scott) 

 Setae of leg 5 normally developed, slender .... I. intermedia Lang 



14. Setae on leg 5 normally developed, long and fine .... I. pusilla Brady 

 Setae of baso-endopodite of leg 5 short, compressed and dagger-shaped; 



those of exopodite short I. aemula (Thompson and A. Scott) 



MALES 



1. Endopodite of leg 1, 3-segmented 2 



Endopodite of leg 1, 2-segmentcd .... I. novaezealandiae (Thomson) 



2. Exopodite and endopodite of leg 1 of nearly the same length (exopodite 



may be implanted much higher than endopodite) 3 



Exopodite as long as, or shorter than, 1st endopodal segment of leg 1 . . 4 



3. 1st segment of endopodite leg 1 twice as long as wide. I. australis Brady 

 1st segment of endopodite leg 1 more than twice as long as wide. 



I. antarctica (Giesbrecht) 



