DISTRIBUTION OF PHYTOPLANKTON 65 



in numbers of more than a hundred thousand, in order of their relative numerical 

 importance. 



This list is intended only for comparison with the results of future surveys. In 

 other years, no doubt, other species will come into prominence and some of those here 

 included will fade into insignificance. It must be realized also that this list does not 

 represent the findings of a whole year, but mainly the results of December and January 

 at South Georgia with the addition of stations in February between South Georgia 

 and the Falkland Islands, and again, a few stations in March and late May on the 

 eastern side of South Georgia. Had many samples been taken earlier in the spring 

 there can be no doubt that Coscinodiscus bouvet and Thalassiosira antarctica would have 

 been very much higher in the list. Again, had samples been taken in February 1926, 

 when so much Thalassiothrix antarctica was taken by the Continuous Plankton Recorder 

 on approaching South Georgia, this diatom would undoubtedly have held a more 

 prominent position. 



Next in importance to the diatoms as a whole comes Halosphaera viridis with a total 

 of 83,866,000, which would place it before Corethron valdiviae in a list of prominence 

 of all phytoplankton organisms. But, as already explained, we have found it exceedingly 

 restricted in distribution. 



Next comes the Silicoflagellate, Distephanus speculum, with a total of 418,000. 



Lastly, the Dinoflagellates, with a total of 282,650 which may be subdivided as 

 follows : 



Peridinium spp. 

 Dinophysis spp. 



233,200 

 I3.3 00 



Ceratium pentagonum 35,800 



Ceratium spp. 350 



COMPARISON OF THE PHYTOPLANKTON OF 

 DIFFERENT REGIONS 



Having described the distribution of the individual species, we may now discuss the 

 phytoplankton as a whole in relation to the different regions and their water masses. 

 A discussion of the actual hydrological conditions governing phytoplankton production 

 will be reserved for a further section following the present one which is primarily 

 topographical. We can divide the area under consideration into three parts: a region of 

 the Southern Ocean to the north-east of South Georgia sampled at four stations 

 (Sts. 9-12) on a voyage from Tristan da Cunha to South Georgia in February 1926; 



