48 



DISCOVERY REPORTS 



indicated by the moderate numbers of Nitzschia seriata and Thalassiothrix autarctica. 

 However, both these forms do occur in surface water of western Weddell Sea origin, 

 and it seems more probable that their presence here, in rather higher proportions than 

 usual for water of this type, may be due merely to the seasonal influence, the species 

 concerned possibly showing a more strongly marked vernal increase in western Weddell 

 Sea water. 



Again, on the line worked eastwards from Cooper Island (Fig. 4) heavy catches with 

 immense numbers of small forms were obtained. The inshore station showed a com- 

 paratively small catch, which was not so rich in species as those taken farther offshore. 

 Even here the volume of the sample reached 250 cc, and in the very minute sub-sample 

 it was possible to examine no organisms other than diatoms were seen. The full analyses 

 of the material from this line will be found in Table XIV; the proportions of the leading 

 forms are indicated in Table 10. 



Table 10 



* Excluding uncountable colonies. f Excluding gelatinous colonies. 



It will be seen that the general character of the phytoplankton was very similar to that 

 taken on the previous line, with Chaetoceros socialis dominant and Thalassiosiro aut- 

 arctica, Fragilaria autarctica, Chaetoceros criophilum and more rarely Ch. neglectiis also 

 numerous, in that order of importance. At the one station where Ch. socialis was not 

 found, St. 511, the large C. criophilum was strongly dominant, and the percentage of 

 Thalassiosira and other forms whose abundant occurrence is characteristic of surface 

 water derived from the western Weddell Sea, showed a marked decrease in com- 

 parison with the other stations on the line. This suggests mixing with eastern type 

 Weddell Sea surface water. Apart from this one station the phytoplankton encountered 



