NOTES ON SPECIES 153 



to invalidate such a comparison. The major quahtative differences between the floras 

 can be seen from the following list of the dominant forms in the two areas arranged in 

 order of importance. 



Weddell Sea area: Bellingshausen Sea: 



Chaetoceros criophilum Corethron valdiviae 



Rhizosolenia styliformis Chaetoceros neglectus 



Nitzschia seriata Nitzschia seriata 



Corethron valdiviae Rhizosolenia ahta f. gracillima 



Fragilaria atitarctica Thalassiothrix antarctica 



Corethron valdiviae (spineless chains) Chaetoceros tortissimus 



Chaetoceros neglectus Fragilaria antarctica f. bouvet 



Thalassiosira antarctica F. antarctica 



Chaetoceros dichaeta Thalassiosira antarctica 



Thalassiothrix antarctica Nitzschia closteriiim 



Nitzschia closteriiim Eucampia antarctica 



Rhizosolenia alata Chaetoceros dichaeta 



It will be realized that there was a fairly close resemblance between the association 

 met with far south in the Weddell Sea, and that in the extreme south-west of the 

 Bellingshausen Sea. Nitzschia seriata, Chaetoceros neglectus and Fragilaria antarctica 

 were prominent at both, together with Rhizosolenia truncata, one of the less important 

 species not listed above. The Bellingshausen Sea association was distinguished by the 

 abundant occurrence of Thalassiothrix antarctica and Fragilaria antarctica f. bouvet. The 

 general similarity in the floras of old Antarctic surface waters immediately to the south 

 of the convergence, irrespective of their history, has already been noted ; it is in the rich 

 intermediate zone lying roughly between 65 and 55° S that the differences are most 

 marked. The possible reasons for this will become apparent when the problems of dis- 

 persal come to be discussed. 



NOTES ON THE SPECIES 



In these notes the species identified during the course of the work are arranged 

 systematically, with a brief account of their distribution within the area and references 

 to the more important literature. It is hoped that the latter will be sufficient to establish 

 the identity of the species concerned. I am greatly indebted to Mr F. W. Mills for 

 checking the references to all the diatom species, for providing some useful additional 

 references, and for advice on various taxonomic points. Both the Antarctic plankton 

 diatoms and the dinoflagellates of the warmer seas are obviously in need of thorough 

 systematic revision, but to do this adequately would be a labour of years. It would, 

 moreover, be outside the scope of the present paper, which merely attempts to describe 

 the more important associations in the different areas, and by correlation with hydro- 

 logical and other data to give some explanation of their distribution and seasonal 

 abundance. 



The Dinoflagellata were poorly represented within the more important Antarctic 

 Zone, the greater number of the species recorded being obtained at the few stations 



