50 DISCOVERY REPORTS 



It will be seen that inshore Choetoceros sociolis and Thalassiosira antorctica were 

 dominant, with lesser numbers of Chaetoceros criophihmi, Ch. neglectiis and Fragilaria 

 antarctica. Among the rarer forms Eucampia antorctica reached its maximum for the 

 line at the innermost station, as on the lines worked farther west. Chaetoceros schim- 

 perianus and Dactyliosolen laevis reached their maximum for the survey at Sts. 506 and 

 505 respectively. The transition to the eastern Weddell Sea surface water evidently 

 began at St. 504. Here the large Chaetoceros criophilmn was dominant with lesser num- 

 bers of Rhizosokm'a styliformis, and the percentage of these two forms, more especially 

 the latter, increased steadily towards the seaward end of the line. All the less numerous 

 forms characteristic of the western Weddell Sea water show a decrease from this station 

 outwards, with the exceptions of Nitzschia seriata and, at St. 503, Thalassiosira ant- 

 arctica. 



It will be noted that on this line Corethron valdiviae was still rare, as on the lines 

 worked in almost purely western Weddell Sea water, in strong contrast to the conditions 

 obtaining in the older eastern Weddell Sea water which was examined on the earUer 

 lines to the north-east, where it was one of the dominant forms. It seems that in the 

 eastern Weddell Sea surface water one encounters successive zones in which first 

 Corethron and then Rhizosolenia styliformis accompany Chaetoceros criophilum as the 

 dominant forms, and that where Rhizosolenia is present in any numbers, as on this line, 

 Corethron is relatively scarce. This can be seen on the Larsen line at Sts. 495 and 494 

 (Tables IX and 5). It was even more clearly illustrated on the line worked south-east 

 from South Georgia later in the season, which is described in the Weddell Sea section 

 (pp. loi, 102). On this Une zones in which either Corethron, Chaetoceros or Rhizosolenia 

 were completely dominant were met with, divided by transitional areas in which 

 either Corethron and Chaetoceros, or Chaetoceros and Rhizosolenia, were more or less 

 codominant. 



Having given some account of the nature of the phytoplankton encountered on the 

 several lines of the November 1930 survey, it remains to give a general view of the flora 

 over the whole area at this time. Separate distribution charts (Figs. 19-30) of the more 

 important species have been constructed, which, coupled with the chart showing the 

 estimated diatom totals, should give a clearer picture of the situation than many pages 

 of detailed description. Some of the rarer forms are of course \tr\ instructive in their 

 distribution, but space precludes a detailed consideration of these. 



The general distribution chart (Fig. 18) shows that the heaviest phytoplankton hauls 

 were obtained to the south and south-west of the island in water of western Weddell 

 Sea origin. The cold tongue of eastern Weddell Sea surface water projecting up the 

 north-east coast was not so rich in individuals. The local eddy off the north-east coast 

 fairly close in had a moderately rich flora, and also the water sampled to the extreme 

 north-east. The poorest hauls were obtained to the north-west in old BeUingshausen 

 Sea water, and to the north, where this water was probably mixing with old water of 

 the eastern Weddell Sea type. 



