MICROPLANKTON 261 



amount of elasticity in the application of the ecological terms is borne in mind, the value of the earlier 

 work seems to me most amply justified (T.J.H.). 



Within the group Soleniineae, consisting almost wholly of holoplanktonic cosmopolitan forms, the 

 difficulty involved in any attempt at further ecological characterization is augmented by the almost 

 completely panthalassic nature of some of the most important species. This results in some species 

 showing maximum importance offshore under oceanic conditions in spring, but inshore under neritic 

 conditions in autumn or vice versa. The compromise implicit in the word panthalassic seems as far as 

 one can go in any attempt at brief summary of their distributional tendencies ! 



Table 26. Relative importance of 

 group. Results arrayed according 

 river line 



the group Soleniineae, and percentage of the several species zvithin the 

 to distance from the land as shown, omitting those from the Orange 



A few species, notably Leptocylindrus danicus with its maximum late in the succession, were definitely 

 limited to the neritic samples in both series. Rhizosolenia setigera, seen only during the spring survey, 

 was important inshore at that season. 



The most completely cosmopolitan species, that helped to render this group dominant offshore in 

 spring and of considerable importance there in autumn also, should probably be regarded as essentially 

 oceanic, but so adaptable that they may attain higher numbers among the vastly heavier catches of 

 other forms in enriched coastal waters on some occasions. A similar difficulty is found when one 

 attempts ecological classification of some of the dominant phytoplankton species of antarctic surface 

 waters (Hart, 1942). 



In the Benguela current area the important panthalassic solenoids were: Rhizosolenia alata and 

 R. hebetata, especially late in the succession inshore, but also augmenting the group's spring maximum 

 offshore; R. styliformis, here showing a more distinct oceanic trend and spring maximum; and 



18-2 



