258 DISCOVERY REPORTS 



the chaetocerids on the 'outer shelf in spring, and to the 'Pennatae' offshore in autumn. Inshore 

 they were relatively unimportant at both seasons. 



(5) The 'Pennatae', though generally much less abundant than the chaetocerids, ranked second 

 to that group at the inshore stations during both surveys. They were rather more important in autumn 

 than in spring right inshore, but this trend was reversed on the 'outer shelf. Offshore the group was 

 relatively much more important in autumn than during spring, although slightly more abundant in 

 the richer spring catches. 



Table 23. Relative importance of the group Discineae, and percentage of the several species, within the 

 group. Results arrayed according to distance from the land as shown, omitting those from the Orange 

 river line 



Average total for each category as per- 

 centage of the average total for the 

 group (M category/6 as %) 



Skeletonema costatum 



Stephanopyxis turris 



Thalassiosira condensata 



T. excentrica 



T. hyalinum 



T. rotula 



T. subtilis 



Thalassiosira spp. non det. 



Bacterosira fragilis 



Coscinodiscus gigas 



C. janischii 



Coscinodiscus spp. non det 



Actinocyclus spp. non det. 



Planktoniella sol 



Hemidiscus cuneiformis 



Actinoptychus senarius 



Asterolampra spp. non det. 



Asteromphalus heptactis 



45'0 



0-3 



54-7 



6-o 

 30-2 



47-3 



6-7 



Table 23, which shows the relative importance of the various Discineae when the data are grouped 

 in this fashion, provides strong evidence of the neritic or inshore habit of most of the species. Though 

 several extended to the outer shelf, eleven out of the eighteen categories were not seen farther offshore. 

 Planktoniella sol was clearly the most essentially oceanic species. Although sufficiently adaptable to 

 occur inshore its numbers increased very markedly with increasing distance from land during both 

 surveys. The remainder of the scanty offshore representation of the group consisted chiefly of more 

 panthalassic, but equally cosmopolitan, species like Thalassiosira excentrica and T. subtilis. 



The most important Discineae inshore were Stephanopyxis turris and various species of Thalassio- 

 sira. They were most prominent in autumn (or late in the succession) while the less numerous forms 

 provided greater relative proportions of the group totals in the smaller spring catches (e.g. Asterom- 

 phalus heptactis). 



