ON COPEPODA FROM CHRISTMAS ISLAND. 181 



corresponding development in Heteraster ohlongus and Sclnzaster 

 is indicated. 



A general description of the growth of compound ambulacrals 

 among the great groups of Echinoids is given ; and, as a result 

 of the facts brought forward, it is argued that " plate-crushing " 

 is due solely to the mechanical " growth-pressure " caused by the 

 development of new plates ; while the appearance of tuberculation 

 corresponding in arrangement with the ambulacral elements is 

 considered to be an aftei'-effect of their fundamental characters, 

 and to modify very slightly, if at all, the structure of the areas. 



EXPLANATION OF PLATE XXVI. 



Fig. 1. Denuded test of EcJiinocardium eordatum, showing the relative smoothness, 



and the crowding of the pores, of ambulacrum III. 

 Fig. 2. The same specimen, after staining and etching, showing the plate sutures, 



particularly in ambulacrum III. 



14. Plankton from Christmas Island, Indian Ocean. — II. 

 On Copepoda of the Genera Oithona and Paroithona. 

 By G. P. Farran.* 



[Received November 5, 1912 : Read February 4, 1913.] 



(Plates XXVII.-XXXI.t) 



Index. 



Geogeaphical Zoology. Page 



Oii^^owffi, spp. of, from Christmas I., Indian Ocean 182 



Paroithona, sp. of, „ „ „ 182 



Systematic. 



Oithona vivida, sp. n., description and figs 183 



Oitho7ia decipiens, STp. n., ,, „ 184 



Oithona fallajc, sp. n., „ „ 185 



Oithona attenuata, sp. n., ,, „ 187 



Oithona simplex, s,p. x\., „ „ 187 



Oithona oculata, sp. n., „ „ 188 



Faroithona pulla, sp. n., „ ,, 190 



Oithona pelagica, Farran, synonym of O. setigera 183 



Oithona tropica, Wolfenden, synonym of O. setigera... 183 



Oithona setigera, Dana, discussion of synonymy of 182 



Oithona, diagnostic table of spp. of 191 



Faroithona, diagnostic table of spp. of 192 



In a previous paper published in the Proceedings of this 

 Society (1911, pp. 282-296), an account was given of the species 

 of Corycceus and Corycella found in a small collection of Plankton 

 made in 1908 by Sir John Murray, K.C.B., F.R.S., and Dr. 0. W. 

 Andrews, F.R.S., at Christmas Island, in the Indian Ocean, and 

 presented to the British Museum by Sir J. Murray. The 

 following account deals with the species of Oithona and Far- 

 oithona found in the same collection. 



* Communicated by Dr. W. T. Calman, F.Z.S. 

 t For explanation of the Plates see p. 193. 



