244 DISCOVERY REPORTS 



groups containing a majority of inshore species, were relatively important. The individual counts 

 show, however, that the oceanic species Planktoniella sol accounted for most of these Discoidae, and 

 the typically offshore species Thalassiothrix longissima and Fragilaria granulata were prominent among 

 the ' Pennatae ', though in that group panthalassic Nitzschia spp. were also numerous. It was here that 



o 



cc 



2 



o 



WSI062WSIObl W5D60 WSIOS9 WSIOS6 WSDS7 



I 



D 

 D 7 



-o 6 

 d 



D 3 



- TOTAL DIATOMS 

 ♦ CHAETOCERACEAE 

 -' "PENNATAE" 



- BIDDULPHIINEAE 

 o DISCINEAE 



SOLENIINEAE 



SO 



OO 



SEA MILES FROM LAND 



Fig. 79. Estimated total diatoms and diatom group totals, survey II. A. Sylvia Hill line, 25-27 September 1950. 



B. Southern Intermediate line, 24-25 September 1950. 



WSD50WSI05I WSIOS2 WSI053 WSI054 

 III II 



-• TOTAL DIATOMS 

 - CHAETOCERACEAE 

 -' "PENNATAE" 

 BIDDULPHIINEAE 



WSIOSS 

 I 



~ 1 1 1 1 1 1 



fO KX) 



SEA MILES FROM LAND 



WSIOS6 



I 



Fig. 80. Estimated total diatoms and diatom group totals, survey II, Orange river line, 21-24 September 1950. 



relatively large numbers of Trichodesmium thiebautii, the filamentous, sometimes colonial blue-green 

 alga most important among the few ' other plants ' in these samples, were met with. 



Finally, the Orange river line showed an extraordinary reversal of the conditions observed during 

 the first survey, the two diatom-rich stations now being found far beyond the projecting shelf-edge 

 at the outer end of the line. Further, they showed a most extraordinary admixture of species. Though 

 oceanic forms such as Chaetoceros atlanticum, C. peruvianum and Planktoniella sol were among the 

 dominants, the essentially coastal Chaetoceros compressum was abundant at station WS 1055. In the 



