418 DISCOVERY REPORTS 



MATERIAL AND METHODS 



The bulk of the material upon which this paper is based consisted of phytoplankton 

 samples obtained in our routine hauls with the Gran international net of 50 cm. 

 diameter, which is fished vertically from 100 to o m. A large majority of these were 

 obtained during the second and third commissions of the R.R.S. 'Discovery II', 

 193 1-5. Information from the earlier sources mentioned in the introduction has also 

 been taken into account, and I have tabulated some earlier data obtained by similar 

 methods, along with those which are presented here for the first time. 1 



During the third commission of the R.R.S. 'Discovery II' I made a preliminary 

 examination of the phytoplankton at almost every station. For this purpose I used a few 

 drops from the catch obtained by a vertical haul with a net of similar type to that 

 recently employed by Harvey (1934) for estimating the quantity of phytoplankton 

 colorimetrically. R. curvata was always noted when present, and in this way, with the 

 aid of the published observations already referred to, a good preliminary idea of the 

 distribution of the species was obtained. This was used in planning the subsequent 

 work. Nearly all our observations falling within its normal range were obtained on 

 cruises to and from the Antarctic Zone, with the stations spaced at regular intervals. 

 In working up the material in detail I examined the Gran net samples from all the 

 stations within the sub-Antarctic Zone, and continued working north and south of the 

 normal range of the species until I had gone three stations beyond its last appearance on 

 each series of observations, except where the series itself did not extend far enough. 

 I believe that this has proved adequate to determine the extreme range of the species. 

 Moreover, almost all the phytoplankton collected during the two commissions, amount- 

 ing to some 750 samples, has been subjected to preliminary examination by Mr D. 

 Dilwyn John or myself, so that there is little chance that any unusual extension of the 

 normal range of so conspicuous a species would have escaped notice. 



The negative evidence obtained in the manner outlined above has not been tabulated ; 

 but the more significant negative records marking the limits of R. curvata on most of 

 the individual lines of stations, have been plotted on the distribution charts. In the 

 Scotia Sea, where many of our hauls containing this species were obtained on lines of 

 stations worked between South Georgia and the Falkland Islands, I have not attempted 

 to plot negative records to the south of the extreme range observed. The large number 

 of phytoplankton analyses from this area already published (Hart, 1934) renders such a 

 procedure unnecessary. 



The preserved samples were worked up by ordinary Hensen counting methods, with 

 the added advantage that as only one conspicuous species was being dealt with, it was 



1 The data so treated have been taken from the tables of phytoplankton analyses published by Hardy 

 (1935) and Hart (1934), and were obtained at the following stations worked by the research vessels: 

 Sts. 137, WS 34, WS 46, WS 68-WS 70, and WS 110-WS 113 from Hardy; and WS 518-WS 523, 633, 

 634 and 648-658 from Hart. The prefix WS denotes stations worked by the R.R.S. 'William Scoresby'; 

 stations without this prefix were worked by R.R.S. 'Discovery' and R.R.S. 'Discovery II'. 



