42 



DISCOVERY REPORTS 



with the exception of the outermost station but one, St. 493, where the temperature 

 was over 0-5° C. higher than at the stations worked on either side of it. This was reflected 

 in the very different character of the phytoplankton present. 



At the innermost station Chaetoceros criophilum was the dominant form, with nearly 

 50 per cent of the total of a very rich haul, and Corethron valdiviae was the only other 

 form of note, while at the next station seawards, this state of affairs was reversed in a 

 haul which, while still heavier than any obtained during the previous survey, was con- 

 siderably smaller than that from the inshore station. At each of the next four stations 

 Chaetoceros criophilum was strongly dominant, forming indeed over 75 per cent of the 

 catch at the next station which, though not the richest in point of numbers, was the 

 largest haul as regards volume taken on this line. At the next three stations, the 

 dominant Ch. criophilum was accompanied by a moderate proportion of Thalassiosira 

 aniarciica. At St. 496 Fragilaria antarctica formed over 10 per cent of the estimated 

 total, and Rhizosolenia styliformis showed an increase both in numbers and in pro- 

 portion to the rest of the catch. At the two succeeding stations to seaward this species 

 formed a trifle over 10 per cent of the phytoplankton estimated, and this in conjunction 

 with the general dominance of Chaetoceros criophilum may be taken as good evidence of 

 the eastern Weddell Sea origin of the water. This brings us to St. 493 where, as has 

 already been shown from a consideration of the temperatures, it is evident that we have 

 to deal with surface water of a different type. The large species were of little importance 

 in the catch from this station, where, in marked contrast to the conditions elsewhere on 

 this line, we find the small forms Nitzschia seriata, Thalassiosira antarctica and 

 Fragilaria antarctica co-dominant. At the outermost station of all Corethron valdiviae 

 predominated, with lesser numbers of Chaetoceros criophilmn and Thalassiosira. This 

 occurrence of Corethron in bulk at the two extremities of the line is paralleled on the 

 Prince Olaf line next to be described. 



The estimated numbers and percentages of the leading forms on the Larsen line are 

 shown in Table 5. 



Table 5 



* Excluding uncountable gelatinous colonies. 



