182 MR. G. P. FARRAX ON 



Of the genus Oithona eleven species were represented. Five 

 of these, 



0. pliimifera, 0. rohusta, 



0. sefigera, 0. nana, 



0. linearis, 



are ah'eady known. The remaining six appear to be unknown 

 and are described below under the following names : — 



0. vivida, 0. attenuata, 



0. decipiens, 0. simplex, 



O.fallax, 0. oculata. 



The closely allied genus Paroithona, previously known from a 

 single species in the N.E. Atlantic, is represented by a new 

 species, P. pulla. 



The fact that twelve species, out of the twenty contained 

 in the two genera, were present will serve to illustrate the 

 remarkable richness of the collection. 



The number of gatherings in the collection was eight. Three 

 of these were taken with nets of larger mesh than the rest, and 

 contained only those species which exceeded 1 mm. in length. 

 The smaller species, including all the new forms, were found 

 exclusively in the other five. 



Holes on the Species. 



Oithona setigera Dana. 



Found in five gatherings and was, next to 0. plimnifera, the 

 commonest species of Oithona. 



This species was described by Dana (8) in 1849, from specimens 

 taken in the Pacific, and Giesbrecht (13) gave a complete 

 diagnosis of it also from Pacific specimens. Most of the Christ- 

 mas Island specimens could be recognised by their large size 

 (1'6 to 1'7 mm., with a few as large as 1*9 mm.), and by the 

 possession of well-marked clavate setae, usually coloured red, on 

 the outer edges of the second basal joints of the swimming-feet. 

 In a few specimens, however, these setfe were long and slender 

 and did not show signs of thickening. These specimens agree 

 with 0. pelagica which I described (11) from the west coast of 

 Ireland, and also with 0. tropica described by Dr. Wolfenden (17) 

 from a single specimen from the Maldives. Other specimens 

 showed a good deal of variation in the amount of the thickening, 

 and in some instances the setae on the fifth pair of feet were 

 thickened and coloured. 



As regards 0. tropica, Wolfenden states that "the inner 

 marginal bristles of the 2nd basals are not swollen as in 0. seti- 

 gera." In this sentence the word " inner" is evidently a clerical 

 error for outer. The proportional lengths of the joints of the 

 1st antennae, as given for 0. tropica, differ from those found in 

 0. setigera, but tlie difference can be explained by supposing the 

 3rd and 4th and the f5th and 7tli joints, the segmentation 



