NOTES ON SPECIES 163 



Chaetoceros castracanei, Karst. 

 Karsten, 1905, p. 116, pi. xv, fig. i. 

 Rather rare and very sporadic in its occurrence ; in all types of Antarctic surface water 

 but as a rule not very far south. 

 Chaetoceros concavicornis, Mangin. 

 Lebour, 1930, p. 122, fig. 88. 

 A few individuals apparently referable to this species were observed at one station 

 just to the south of the sub-tropical convergence. 



Chaetoceros criophilum, Castr. 



Mangin, 1915, pp. 34-6, figs. 13, 14; Hustedt, 1930, p. 667. 



Hustedt is satisfied that Mangin's distinction between this species and the northern 

 Ch. criophilus, Castr., of Gran, is correct. The name should properly be applied ex- 

 clusively to the Antarctic form (Mangin, 1917). 



This is one of the most widespread and abundant of all the Antarctic plankton 

 diatoms. It was often dominant in water of the eastern Weddell Sea type, and was 

 abundant also in the mixed water south and west of South Georgia during the spring 

 survey. It was of frequent occurrence in the Bellingshausen Sea also, but was not nearly 

 such an important constituent of the phytoplankton there. It appears to reach its 

 optimum in somewhat lower latitudes, and late in the season has often been observed 

 north of the Antarctic convergence, in an apparently dying condition. 



Chaetoceros cruciatum, Karst. 



Karsten, 1905, p. 116, pi. xv, fig. 5. 



Rarely, in old Antarctic surface water. 

 Chaetoceros curvatum, Castr. 

 Mangin, 1915, p. 36, figs. 15, 16. 



Present at a few stations in all types of Antarctic surface water, always in small 

 numbers. 



Chaetoceros decipiens, Cleve. 

 Lebour, 1930, p. 126, fig. 91. 



A few individuals, agreeing exactly with this northern form, were observed at one 

 station in sub-Antarctic water. 

 Chaetoceros dichaeta, Ehrb. 



Mangin, 1915, pp. 37-45, figs. 17-26. 



This variable species was found to be very characteristic of the phytoplankton far to 

 the south in the Weddell Sea, and in the extreme south-west of the Bellingshausen Sea. 

 It was also abundant on the spring survey round South Georgia, and at a few other 

 stations in comparatively old water in the Scotia Sea. In no case was it found to be the 

 most numerous species, but at the stations indicated was present in uniformly large 

 numbers. 



