246 DISCOVERY REPORTS 



farther inshore, without, however, forming any significant proportion of the vastly richer vegetation 



present there (cf. Figs. 93-5). 



Figs. 81 and 82 show the outstanding importance of the group Chaetoceraceae in the rich coastal 

 waters during both the seasons studied, and the relative narrowing of that zone in spring as compared 

 with autumn (1st survey). Comparison with Figs. 57 and 65 shows how large a proportion of the total 

 microplankton observed inshore was composed of the members of this one group of diatoms. 



20°- 



yiMOWE POINT 



25°- 



S " 



8 



T 

 H -I 



3C* 



NIL I I 

 <|0«Q 



I0-I0 5 {g5 



WALVIS BAY 



ID' 



■SYLVIA HILL 



ORANGE 

 A. 



SURVEY : I 



EAST 



Fig. 83. Distribution of Planktoniella, survey I, March 1950. 

 (Station numbers are shown in Fig. 1.) 



EAST 



Fig. 84. Distribution of Planktoniella, survey II, September- 

 October 1950. (Station numbers are shown in Fig. 2.) 



The distribution of the one discoid species found to be most numerous in the scanty offshore 

 phytoplankton — Planktoniella sol — is shown in Figs. 83 and 84. The finger-like extensions towards 

 the coast shown near the northern limits of the rich coastal upwelling area seem fairly indicative of 

 actual intrusions of oceanic waters, conforming with hydrological data assessed quite independently 

 (cf. Rayner in Gunther, 1935; Hart, 1953 and Fig. 95 below). 



In contrast to Planktionella most of the Discineae observed on these two surveys were distributed 

 mainly inshore or over the continental shelf. The distribution of Stephanopyxis turris, one of the most 

 numerous of these, is shown in Figs. 85 and 86. It can be seen that though it was clearly an essential 

 coastal form, both in autumn and spring, Stephanopyxis was absent from the middle of the Chaetoceros 

 zone at both seasons. Further, it was distributed rather more to the northward in spring (Fig. 86) 



