298 DISCOVERY REPORTS 



Cells usually solitary, but may form short chains. In the solitary forms the cells in 

 girdle view appear somewhat octagonal. Valve surface flat, with small median inflation. 

 The valve mantle slopes obliquely to the connective zone. Bristles emerge within the 

 edge of the valve and proceed in a direction parallel with the pervalvar axis of the cell. 

 Bristles short, rotund, apiculate-globiform. At the point of emergence the bristles are 

 strongly inflated and continue gradually narrowing to an attenuated apex, apices slightly 

 convergent. When in chain formation these globiform bristles are found only upon the 

 lower valve of the terminal cell. The bristles of the other cells are somewhat thickened 

 at the point of emergence, but taper gradually to a fine point. All bristles in the chain 

 are directed towards the posterior end of the chain. Chromatophores : numerous short 

 vermiform bodies penetrating the bristles. Diameter of valve 40-46/^ 



The majority of the specimens observed were of the solitary type. A characteristic 

 diatom of the southern seas, probably found only in cold water. It was observed fairly 

 frequently between the South Shetlands and Cape Horn. 



Observed at Sts. 383, 384, 453, 480. 



Chaetoceros Schimperianum Karsten. (PI. XIII, figs. 13, 14.) 

 Karsten, 1905, p. 117, pi. 15, fig. 2, pi. 16, fig. 4. 



Cells usually united to form short chains, three to twelve cells in a chain, sometimes 

 solitary. Valves elliptical, valve surface flat but may be weakly concave. Bristles emerge 

 well inside the girdle, and proceed obliquely for a short distance and then continue 

 almost at right angles to the chain axis. Bristles a little swollen at the point of emergence 

 but taper to hair-like extremities. The bristles undulate gently, often appearing to cross 

 those of the neighbouring cell, not only at the place of emergence, but sometimes at one 

 or even two other points, often at a point midway between the cell and the tip of the 

 bristle, and sometimes after crossing the bristles again converge and may meet and cross 

 again at the extremities. Foramina narrow, hexagonal. Chromatophores: numerous 

 small cocciform bodies penetrating the bristles. Diameter of valve 12-20/x. 



A neritic form characteristic of the Antarctic Ocean, probably never extending north 

 of 45 S. Favours low salinity and cold water. It was observed, but never in great num- 

 bers, around South Georgia and in the Weddell Sea. 



Observed at Sts. 478, 479; WS 550, 551, 552 a. 



Subgenus Hyalochaete 

 Section Oceanica 



Chaetoceros decipiens Cleve. 



Cleve, 1873 b, p. 11, pi. 1, fig. 5- 



Gran, 1905, p. 74, fig. 88. 



Meunier, 1910, p. 219, pi. 25, figs. 12-17. 



Hustedt, 1930, p. 675, fig. 383. 



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



Chaetoceros Grunozvii Schiitt, 1895, p. 43, pi. 4, fig. 14. 



