SYSTEMATIC ACCOUNT 257 



of puncta, from which radiate numerous lines of rather coarse puncta. These lines are 

 either long or short, some consisting of a few dots only, but all fail to reach the margin 

 of the valve, leaving what appears to be under a low power objective a hyaline mar- 

 ginal band. The lower valve has also a central ring of granules, from which radiate lines 

 of puncta, lines usually less dense and less numerous, approaching more closely to the 

 valve margin, but seldom if ever joining it. Margin strong, sometimes finely striate. In 

 this species I include also Char cotia Janus var. plana M. Peragallo, as I found it was im- 

 possible to separate them. C. Janus M. Peragallo might be considered as a separate 

 species, but I find that the small prominences placed in a circle near the margin are very 

 variable in form and number, and I feel that this feature is too inconstant to be made 

 a specific character. 



A small species widely distributed throughout the Southern Ocean, seldom found in 

 great numbers, most probably oceanic. 



Observed at Sts. 461, 463, 479, 512, 551, 552, 560, 570, 575, 576, 578, 661 ; WS 481. 



Genus Planktoniella Schiitt 

 Schiitt, 1893 



Planktoniella sol (Wallich) Schiitt. (PL XIII, fig. 1.) 



Schiitt, 1893, p. 20, fig. 8. 



Karsten, 1907, p. 369, pi. 39, figs. 1-11. 



Lebour, 1930, p. 50, pi. 1, fig. 5. 



Hustedt, 1929, p. 465, fig. 259. 



Coscinodiscus sol Wallich, i860, p. 38, pi. 2, figs. 1-2. 



Planktoniella Woltereckii Karsten, 1905, p. 157. 



Cells discoid, consisting of a central " coscinodiscoid " body surrounded by a wing- 

 like expansion of peripheral loculi. Central or valvar portion small, valves convex, 

 covered with large polygonal areolation arranged in tangential curved lines, somewhat 

 similar to the structure of Coscinodiscus excentricus. The extracellular expansion is 

 divided into a varying number of loculi by radial rays. These chambers may be turgid or 

 flaccid. It is probable that by controlling the turgidity of the peripheral loculi, the 

 organism has the power to alter its habit from that of a bottom form to a pelagic one. 

 The photosynthetic elements are restricted to the valvar portion of the organism. 

 Chromatophores : several plate-like bodies. Diameter of valve portion 30-180^, total 

 diameter often as much as 360^. 



The ratio between the diameter of the valvar portion and the total diameter of the 

 organism (including the wing-like expansion) differs very considerably. It was noticed 

 that the specimens in the neighbourhood approaching the Antarctic convergence 

 (Sts. 450, 451, 452) possessed very small valvar portions and relatively large peripheral 

 wings. Often the valve measured less than one-fifth of the total diameter. The loculi 

 were numerous but narrow. Those specimens observed from tropical stations, par- 

 ticularly those to the north of Madagascar were very large in the valve portion and large 

 also in the wing expansion, but the diameter of the valve was usually half the total 



