MAIN TYPES OF PHYTOPLANKTON 



23 



scantiest of hydrological data to assist him, and that he was not aware of the existence 

 of the Antarctic convergence. He apparently took the extreme northern range of the 

 majority of the southern forms as the limit of his cold region, and as we have seen that 

 typically Antarctic species are often carried north of the convergence in small numbers, 

 this limit naturally approaches the sub-Antarctic more closely than the Antarctic con- 

 vergence. If one examines Mangin's actual analyses, one finds that the distribution of 

 C.fusus is as shown in Table 3. 



Table 3 



It will be seen that at ten out of the fourteen stations at which it was found C. fiisus 

 occurred in either sub-Antarctic or sub-tropical water. The only justification for Mangin 

 regarding it as a cold-water form was that he was unaware of the big sweep southwards, 

 beginning approximately in long. 45" W, which the Antarctic convergence takes on 

 rounding the Horn. Even so he has recorded it from four tropical stations which he does 

 not mention in the text. The main point is that Mangin's findings, when reviewed in the 

 light of modern hydrological work, confirm the fact that the maximum occurrence of 

 C.fusus in the South Atlantic is reached in the vicinity of the sub-tropical convergence. 

 A somewhat similar distribution in the North-east Atlantic, where the boundary between 

 sub-polar and sub-tropical water is less well defined, owing to the action of the Gulf 

 Stream, is suggested by Lebour's brief remarks (1925, p. 146) concerning this species. 

 We agree with her that the warm-water forms are in general smaller and more slender 

 than those of sub-polar waters, but as previously stated, owing to the presence of inter- 

 mediate forms in our material, the retention of the sub-species seta, as by Mangin, 

 seems hardly justified. 



A similar distribution of C. fiisiis was found by the ' Valdivia ' farther to the eastward 

 in the South Atlantic, as is evident from the extracts from Schimper's notebook quoted 

 by Karsten (1905, p. 35). These are considered later in relation to their bearing upon 

 the part played by the "warm deep" water in the economy of the Southern Ocean. 



