142 DISCOVERY REPORTS 



line. From the description of the other work in this area, it will be gathered that these 

 species were not frequent in the east of the Bellingshausen Sea, but were often abundant 

 in the rich and varied associations to the south-west. Their occurrence at the outermost 

 stations on this line is therefore in good agreement with the general idea of the north- 

 easterly drift of the surface water. 



SUMMARY 



The general character of the phytoplankton from the twenty stations worked in the 



BeUingshausen Sea during the season 1929-30 is summed up in the following list, which 



gives the twelve leading forms in order of their total abundance, with the number of 



stations at which each was observed, and their percentage of the total phytoplankton. 



Chaetoceros socialis in uncountable colonies was dominant at St. WS 502 and is not 



included in this list. 



Total % 



Corethron valdiviae (20) 

 Chaetoceros neglectus (7) 

 Rhizosolenia alata f. gracilUma (18) 

 Chaetoceros tortissimus (2) 

 Nitsschia dosterium (6) 

 A^. serial a (16) 

 Thalassiosira antarctica (15) 

 Eiicampia antarctica (8) 

 Biddidphia striata (11) 

 Chaetoceros criophilum (15) 

 Rhizosolenia triincata (6) 

 Fragilaria antarctica (8) 

 Other forms 



Total phytoplankton estimated 221,084,600. 

 * Due mainly to St. WS 501. f Due in part to St. WS 504. 



It will be seen that the position of many of these forms is due mainly to the very 

 rich haul taken at St. WS 501 in the mouth of Neumayr Channel, which was of the 

 special type found at a few other stations among the Palmer Archipelago, and by no 

 means characteristic of conditions in the Bellingshausen Sea proper. Leaving these 

 forms out of consideration, it is apparent that Corethron valdiviae and Rhizosolenia 

 gracilUma were very markedly dominant in the north-eastern Weddell Sea at this time. 

 If we leave St. WS 501 out of account the estimated total phytoplankton becomes 

 157,033,400 for nineteen stations or an average of 8,264,900 organisms per station. 

 Bearing in mind that the hauls obtained at the few stations worked early in the year 

 were comparatively poor, it becomes very evident that a rich development of what may 

 be called the Corethron — Rhizosolenia gracilUma association was taking place late in the 

 summer, as this average considerably exceeds that obtained for stations in the same area, 

 worked in the January of the following year. This increase to the north-east of the 

 Bellingshausen Sea may be the precursor of the autumnal development in older surface 

 water of Bellingshausen Sea origin farther to the northward. 



