COPEPODA FROM CHRISTMAS ISLAND. 183 



between wliich is imperfect, to be united and the 8th and 10th 

 joints each to have been divided into two. 



It seems, then, that 0. i^elagica and 0. tropica cannot be main- 

 tained as species distinct from 0. setiyera, but the fact is worth 

 noting that, in the N.E. Atlantic, 0. setigera, whether the cause 

 be racial or environmental, is not found with thickened setee, 

 while in tropical regions these setfe are almost alwaj's present. 



In addition to the lai'ge form mentioned above there occurred 

 a very few specimens of a form measuring from 1-20 to 1"26 mm. 

 in length. These are the same size as, and, at first sight, look very- 

 like 0. plumifera, but examination of the appendages shows that 

 they agree with 0. setigera. The setse of the basal joints of the 

 swimming-feet are not thickened. There did not appear to be 

 any specimens of intermediate size connecting the larger and 

 smaller forms. 



Distribution. Nortli Atlantic, Gulf of Guinea, Mediterranean, 

 Gulf of Suez, Indian Ocean, Pacific Ocean. 



OlTHONA PLUMIFERA Baird. 



Present in all the gatherings and very common in most 

 of them. 



Almost all the specimens bore tufted plumose outer-edge setfe 

 on the 2nd basal joints of the first three pair of swimming-feet, 

 and in the few cases where they were absent it seemed probable 

 that the plumose tip of the seta had been broken off. The 

 amount of feathering varied in different specimens. In most 

 cases it was opaque and of a bright red colour ; in others it was 

 transparent and colourless and difficult to observe. In the 1st 

 maxilla there was no seta on the 2nd inner lobe and the seta 

 on the endopodite was very minute. The endopodite of the 

 mandible bore only three setae. The size of the specimens varied 

 from 1"20 to 1-37 mm. 



Distribution. Mediterranean, Gulf of Guinea, Red Sea, Arabian 

 Sea, Indian Ocean, Pacific Ocean, Gulf of California, off Cape of 

 Good Hope. 



OiTHONA LINEARIS Giesbrecht. 



This easily recog]iised species was present in six gatherings, 

 being almost as common as 0. setigera. 



Distribution. Red Sea, Indian Ocean, Pacific Ocean, 



OlTHONA VIVIDA, sp. n. (PI. XXVII. figs. 1-8.) 



Female (fig. 4). — Length •68--74 mm.; cephalothorax '37 mm.; 

 abdomen "34 mm. ; proportional lengths of abdominal segments 

 and f urea 15:40:22:18:17:15. 



Rostrum (fig. 5) shai-p-pointed and produced anteriorlj^, as in 

 0. plumifera and 0. setigera. 



1st antenna (fig. 1) very slender, reaching to the genital 

 openings ; proportional lengths of antenna! joints : 



12 3 4 5 6 78 t) 



11 9 8 + 3+10 17 53 l]+!23 o 9 KC 



