286 DISCOVERY REPORTS 



NOTES ON THE SPECIES 



The following notes on the species and categories included in the grouping system 

 are intended to facilitate comparison of the data presented here with previous work. 

 They are arranged in order of the ecological groupings, not taxonomically. Only the 

 most important synonymy is given, and the generic and specific names adopted are 

 those used by Hendey (1937). 



Group I 

 Fragilariopsis antarctica (Castracane) Hustedt in Schmidt (Hendey, 1937, p. 332) 



=^Fragilaria antarctica Castracane (1886); Hardy in Hardy and Gunther, 1935; 



Hart, 1934. 

 The most numerous diatom in Antarctic seas, taking the year as a whole, and 

 certainly one of the most important producers despite its small size. Very long curved 

 chains are developed when growth is rapid, which break up in preserved samples. Its 

 abundance in all parts of the Antarctic zone throughout the year makes it seem certain 

 that F. antarctica is not necessarily dependent upon a solid substratum at any stage and 

 may therefore be considered as 'oceanic'. It is, however, one of the species most 

 commonly found alive in the pack-ice and hence provides a good illustration of a 

 species which confounds rigid application of the Haeckellian terminology (cf. Hendey, 

 1937, p. 227, where it is tabulated as both oceanic and neritic, holoplanktonic and mero- 

 planktonic). The strongly silicified frustules are very resistant, and are the most 

 plentiful recognizable remains in the stomachs of herbivorous zooplankton, in diato- 

 maceous oozes and muds, and in the guano of carcinophagous birds. 



Nitzschia seriata Cleve (? + A^. delicatissima Cleve). 



Among those who have studied Antarctic material in recent years, Hendey, Hardy 

 and myself have not been convinced that N. delicatissima occurs there. Very thin forms 

 are to be found, especially far south among pack-ice, but there appears to me to be 

 a continuous but somewhat irregular gradation in width of the cells from north to 

 south, ranging from typical N. seriata of the largest size downwards. Workers in the 

 northern hemisphere record both species as reaching their greatest abundance near the 

 junction of Atlantic and polar waters, with a tendency for N. seriata to be the more 

 polar of the two (Braarud, 1935, p. 97, and others). I believe that we are almost 

 certainly dealing with phases of one species N. seriata in the far south, but prefer to 

 use the indefinite heading so long as any doubt exists. Since the organisms so described 

 have the same time distribution, the possibility of confusion is unimportant in broad 

 considerations of the phytoplankton population as a whole such as are attempted here. 

 Hendey (1937, p. 352) is probably wrong in regarding this species as neritic. We find it 

 in the open ocean at all seasons, though it is certainly most abundant in neritic areas. 

 It is much more of a summer form than Fragilariopsis, but has been found alive in 

 pack-ice. I would certainly regard it as oceanic in the sense the word is used in this 



