PELAGIC PLANT LIFE 



353 



has, however, encountered one solitary case where plankton 

 algae could be employed for this purpose. Biddulphia sinensis 

 (Fig. 248), a neritic diatom from the coasts of the Indian Ocean, 

 was met with in the North Sea for the first time in 1903, to 

 begin with in the southern parts, and then gradually farther 

 and farther north, until at last it was discovered on the west 

 coast of Norway at Bergen. Its travelling rate corresponds 

 to the values which have been otherwise obtained for the 

 velocities of the current along the coasts of Denmark and 

 Norway. Latterly, it has found a fixed distribution-centre in 

 the north-eastern corner of the North Sea, whence it extends 



still farther northwards every 

 autumn. The velocity of the 

 current could hardly be deter- 

 mined from the observations of 

 these last few years, as there is 

 always the possibility that this 

 diatom has more than one 

 centre of distribution, but its 

 annual wanderings clearly in- 

 dicate the direction of the 

 current. 



A large quantity of plankton 

 algae has been collected during 

 the "Michael Sars " Expedi- 

 tion along the whole route, and 

 will contribute valuable infor- 

 mation regarding the distribu- 

 tion of the different species. We have been particularly 

 successful in our study of the coccolithophoridae, owing to the 

 improved methods we were able to adopt. I shall deal 

 separately with their distribution in what follows, and at the 

 same time give some particulars of their quantitative occur- 

 rence. Part of the material is still incompletely examined. 

 The difficult species of Peridinium in particular, and of a few 

 other genera, will require a separate monograph for their special 

 treatment ; we have secured immense numbers of these forms. 

 In other respects our observations practically confirm the 

 views regarding the distribution of species that we owe chiefly 

 to Cleve. 



I shall now give a preliminary description of the character of 

 the plankton along our route, founded upon an examination of 



Fig, 248. — Biddulphia sinensis (^ 

 (Ostenfeld.) 



Phytoplank- 

 ton collected 

 during the 

 " Michael 

 Sars " Ex- 

 pedition. 



