82 DISCOVERY REPORTS 



Chaetoceros atlanticus. Still farther north, at St. 647, the phytoplankton was found to 

 be very rich, with Ch. neglectus strongly dominant, and Nitzschia seriato, Fragilaria 

 antarctica, Chaetoceros atlanticus and Ch. dichaeta next in order of importance. This 

 haul was by far the heaviest obtained on the whole of this line. 



The considerable rise in temperature at the next station, 648, indicates that it was 

 worked only a short distance to the south of the Antarctic convergence. The phyto- 

 plankton here showed a great falling off in bulk, but was still rich numerically owing to 

 the pronounced dominance of the minute Nitzschia seriata. The only other forms of 

 much importance were the spineless chain form of Corethron valdiviae and Fragilaria 

 antarctica. Among the rarer forms more typical of sub-Antarctic conditions Rhizosolema 

 ciirva and R. polydactyla made their first appearance, together with various dino- 

 flagellates. In point of fact these species were actually more numerous here than at the 

 definitely sub-Antarctic stations farther north on this particular line, so that despite 

 their more abundant occurrence in sub-Antarctic water at other times it should be 

 recognized that under certain conditions they may show a maximum in the com- 

 paratively warm, old Antarctic surface water immediately to the south of the con- 

 vergence. A somewhat similar circumstance seems to have been noted by Schimper, 

 when he recorded R. curva as the dominant species in a surface haul some distance to 

 the south of the convergence, north-west of Bouvet Island, comparatively early in the 

 year (Karsten, 1905, p. 37). 



At St. 649 the much higher temperature and salinity indicates clearly that the 

 Antarctic convergence had been crossed. The phytoplankton was poor, with the spine- 

 less chain form of Corethron valdiviae, Nitzschia seriata and Dactyliosolen antarcticus the 

 most numerous species. Rhizosolenia curva was present in small numbers. Again at 

 St. 650 the phytoplankton was very scanty. Here Nitzschia seriata was dominant, and 

 among the other forms Corethron valdiviae (spineless chains), Ceratium pentagomm and 

 Dactyliosolen antarcticus were slightly the more numerous. The two typically sub- 

 Antarctic species of Rhizosolenia were both present in small numbers. At the northern- 

 most station on the line Chaetoceros atlanticus was the most numerous species in an 

 extremely poor catch of Antarctic stragglers. 



As the ship proceeded eastwards from Staten Island to South Georgia, a few stations 

 were worked, mainly to the north of the Antarctic convergence and in the area of the abrupt 

 curve which it makes to the westward of the Shag Rocks. The analyses of the phyto- 

 plankton material collected on these stations are given in Table XXIII. It will be seen 

 that at all of them the phytoplankton was very scanty, and consisted for the most part 

 of Antarctic stragglers. Of these the most important were Dactyliosolen antarcticus, 

 Corethron valdiviae, Chaetoceros atlanticus and Nitzschia seriata. At the eastern end of 

 this line Chaetoceros criophilum also made its appearance. Rhizosolenia curva was taken 

 in small numbers at almost all of these stations, including the most easterly one, St. 658, 

 which was worked in Antarctic surface water. 



In attempting to epitomize the main features of the results obtained during March 

 1 93 1, recourse has been had to distribution charts rather than to a more detailed con- 



