352 DISCOVERY REPORTS 



This species was described first by H. van Heurck (1909) as a variety of Nitzschia 

 Ostenfeldii, but Peragallo pointed out the essential differences between them, and 

 raised van Heurck's variety to specific status. In this I agree with Peragallo. 



Observed near St. 560. 



Nitzschia closterium (Ehrenberg) Wm Smith. (PI. XI, fig. 1.) 



Smith, 1853, p. 42, pi. 15, fig. 120. 



Lebour, 1930, p. 212, fig. 176. 



Ceratoneis closterium Ehrenberg, 1840^, p. 144. 



Cells solitary, not united to form chains, but often found in enormous masses. The 

 shape of the cell may vary considerably, but generally the main or central portion is 

 weakly oblong with the ends tapering off gently to form the long hair-like apices, or 

 shortly crescentic, or fusiform, with the characteristic attenuate apices. The apices vary 

 in length considerably, and one is usually bent slightly. Chromatophores : two flattened 

 bodies. Apical axis of cell up to 8o/-t. 



A neritic species, widely distributed around the Atlantic coasts of European countries. 

 It was observed occasionally around South Georgia and the South Sandwich Group. 



Observed at Sts. 304; WS 542, 543. 



Nitzschia pelagica Karsten. 



Karsten, 1905, p. 129, pi. 18, fig. 10. 



Cells large, elliptic-lanceolate, apices acute. Raphe central, distinct. Striations very 

 fine, uniform. Connective zone deep, simple. Chromatophores : numerous vermiform 

 bodies, nucleus central. Apical axis of cell 70-270/x ; transapical axis 22-40 /x. 



A large form of Nitzschia, often found in considerable numbers, most probably 

 neritic. It was observed frequently around South Georgia. 



Observed at Sts. 475, 477, 479, 508; WS 550. 



Nitzschia seriata Cleve. 



Cleve, 1883, p. 478, pi. 38, fig. 75. 

 Gran, 1905, p. 129, fig. 174. 

 Lebour, 1930, p. 213, fig. 178. 



Cells narrow, linear-lanceolate, apices acute ; united to form short, stiff chains, by the 

 cells lying together almost point to point. Markings very difficult to see. Chromato- 

 phores: numerous small granules. Apical axis of cell 40-70^ ; transapical axis 6-8 p. 



A small neritic species often found in enormous numbers; very common around 

 South Georgia, Drake Strait, and in the Bellingshausen Sea. 



Observed at Sts. 260, 302, 303, 304, 378-385, 388, 434, 463, 475, 478, 479, 480, 482, 

 502, 503, 508, 570, 575, 576, 577, 580, 670; WS 469, 474, 542, 543, 545, 547, 548, 549, 

 593, 601, 602, 700, 701, 703, 705, 706, 709, 710. 



