64 DISCOVERY REPORTS 



Dinophysis. 



Two species of Dinophysis have been met with but were not abundant: D. ovum, 

 Schiitt., at Sts. 133, WS 35, WS 36, WS 40 and WS 45, and D. tuberculoid, Mangin, at 

 WS67. 



Ceratium. 



C. pentagonum, Gourret, was the only species of the genus met with in any numbers. 

 The form longisetum was taken at odd stations on both sides of the island ; but between 

 South Georgia and the Falkland Islands, where this species was more abundant, the 

 form grandis occurred in greater numbers, and at two stations, 68 and 70, apparently 

 intermediate forms were taken. For their distribution, see Appendix I. 



C. gibberum, Gourret?, a single specimen was taken at WS 70. 



C. tripos atlantica, f. neglecta, Ostenfeld (Paulsen), was taken in small numbers at 

 WS no in water of Weddell Sea origin. 



PROTOCOCCOIDEAE 



Halosphaera viridis, Schmitz, was only taken at three stations close to South Georgia, 

 where it was particularly abundant; these stations lay adjacent to one another to the 

 southward of the island: WS 40, 35,802,000 (5967); WS 43, 18,144,000 (3024) and 

 WS 44, 28,800,000 (4800). It was also taken in smaller numbers at St. 161 far to the 

 south-west of the island, 120,000 (20). 



CHRYSOMONADINEAE 



Whilst Phaeocystis was not taken in the region under consideration in the present 

 survey, it may be of interest to note that it was taken in large quantities by the Con- 

 tinuous Plankton Recorder on November 13, 14, 19 and 20, 1926, in approximately the 

 same latitude as South Georgia, but far to the eastward in the region of Bouvet Island ; 

 i.e. from 52 29' S, 9 48' E to 53 37' S, f 45I' E and from 53 06' S, i° 29' W to 

 5 2°47'S, 2°4i'W. 



SILICOFLAGELLATA 



Distephanus speculum (Ehr.) Haeckel, was recorded at a number of stations, particularly 

 to the south and west of the island. Its distribution is shown in Appendix I. Another 

 species of Distephanus was recorded at WS 45, but was not identified. 



RELATIVE IMPORTANCE OF THE DIFFERENT ORGANISMS 



In the introduction to this section on the phytoplankton, p. 40, reference has already 

 been made to the relative importance of the four groups of phytoplankton. The diatoms 

 are far and away the most important, being present in fifty-seven N 50 V samples to 

 an estimated grand total of close on two thousand million. 



We will now place the twenty more prominent species of diatoms, those occurring 



