DISTRIBUTION OF PHYTOPLANKTON 



55 



recorded by Mangin were present with the more typical stouter forms. Some forms 

 bore the short spine typical of northern forms, others bore a much longer and more 

 delicate spine which might incline one to believe that one was dealing with a separate 

 species did one not often come across forms which bore a short spine at one end and a 

 long delicate spine at the other. 



Rh. truncata, Karsten, was taken in small numbers at three stations to the south- 

 west of the island: WS 40, WS 44 and WS 45. 



53' 



50° 



FALKLAND Is. 



D< 10.000 

 □ 10.000-50.000 

 I 50.O00 -I0O.OO0 



□ 



100,000-500.000 



I 

 500.000 - 1.000.000 



1.000.000-50.000,000 



□ 



uviiT of 



-^ 



4? 



s& 



1Z& 



&J 



□ 



■IV 



•°«1 



ORG I A 



:V, 



SO' 



45° 



Fig. 25. Distribution of Rhizosoknia styliformis at stations between South Georgia and the Falkland Islands, 

 February 1927. The values shown at the seven points immediately around South Georgia represent average 

 values for the stations on the seven radiating lines. Negative observations shown as dots. 



Chaetoceros. 



Twelve species of this genus were recorded. 



Ch. atlanticus, Cleve, was important at only a few stations: notably at St. 161 where 

 over six million were taken. Its distribution is shown in Appendix I. 



Ch. castracanei, Karsten, was also taken in large numbers at St. 161, 444,000 (74) and 

 nearer South Georgia only on the eastern and southern side, i.e. in water of Weddell Sea 

 origin: St. 137, 22,800 (38); St. 138, 600 (6); WS 34, 17,000 (17); WS 36, 5400 (18) 

 and WS 37, 800 (4). 



Ch. criophilam, Castr., was one of the more important diatoms in the survey occurring 

 on all sides of the island. Its distribution is shown in Appendix I and Fig. 26. Mangin 

 (1917) has shown that this species is quite distinct from Ch. criophilum, Gran, a northern 

 diatom, which he has renamed Ch. concavicornis. 



Ch. cruciatus, Karsten, was found at only two stations on the west side of the island : 

 WS 40, 198,000 (33) and WS 44, 54,000 (9). 



Ch. curvatus, Castr., occurred at fourteen stations and was distributed on both sides 

 of the island: see Appendix I. 



Ch. dichaeta, Ehr., and its variety tenuicornis, Mangin, have occurred irregularly on 



each side of the island; their distribution is shown in Appendix I. 



8-2 



