22 



DISCOVERY REPORTS 



time of year at which the collections were made and partly, as will be shown later, to the 

 fact that the eastern Weddell Sea water, which formed the representative of Antarctic 

 surface waters at the southern end of this Une, is characterized by marked predominance 

 of a few large forms, notably Chaetoceros criophilum, Rhizosolenia styliformis and 

 Corethron valdivioe. 



Table 2 



THE PHYTOPLANKTON OF SUB-ANTARCTIC 

 SURFACE WATERS 



This was but poorly represented on the line of stations in 30° W, the small catches 

 at the two stations 670 and 671 consisting mainly of an overlap of typically Antarctic 

 forms. There was no trace of the comparatively rich Rhizosolenia plankton found earHer 

 in previous seasons farther west, probably owing to the time of year. Most of the Ant- 

 arctic forms recorded were in a dying condition, and the only noticeably dominant forms 

 were an indeterminate species of Nitzschia and Ceratium fusus at St. 671. 



The distribution of C. fusus (Table I) is very interesting. It will be seen that it 

 occurred in small numbers at most of the stations north of the Antarctic convergence, 

 but reached its maximum here in 43° S. Mangin, in his account of the Scotia material 

 (1922, pp. 32 and 68), mentions the sub-species seta as particularly abundant in 40° 22' S 

 farther to the eastward. It has been found impossible to distinguish this variety or sub- 

 species satisfactorily, owing to the number of apparently intermediate forms in our 

 catches, a remark which applies to most of the named varieties of Ceratium found in 

 warm seas ; but apart from that the agreement as to the maximum occurrence of the 

 species under consideration, towards the northern limit of the sub-Antarctic surface 

 water, is striking. Mangin's statement concerning the distribution of this species (loc. 

 at., p. 68) is somewhat misleading. He says it was taken at sixteen stations, always in 

 the cold region. It must be realized that in his pioneer work Mangin had only the 



