2 9 o DISCOVERY REPORTS 



cold seas ; generally speaking it is found that tropical species are relatively large in the 

 body of the cell, and possess small and thin appendages, while polar species are very 

 much reduced in the size of the cell, and possess relatively large and complex ap- 

 pendages. 



The gender of the generic name has been changed by authors from time to time, 

 Hustedt, Gran, Lebour and Cleve have considered it as masculine and have terminated 

 the specific epithets accordingly. Castracane and Karsten followed Ehrenberg in 

 making Chaetoceros a neuter noun. The generic name is used here in the gender 

 ascribed to it by its author. 



Subgenus Phaeoceros 

 Section Atlantica 



Chaetoceros atlanticum Cleve. 



Cleve, 1873 b, p. 11, pi. 2, fig. S. 



Gran, 1905, p. 64, fig. 74. 



Hustedt, 1930, p. 641, fig. 363. 



Karsten, 1905, p. 115, pi. 15, fig. 9 



Lebour, 1930, p. m, fig. 77. 



Chaetoceros dispar Castracane, 1886, p. 76, pi. 8, fig. 6. 



Chaetoceros audax Schiitt, 1895, p. 47, pi. 5, fig. 25. 



Chaetoceros polygonum Schiitt, 1895, p. 46, pi. 5, fig. 24. 



Cells united to form chains, chains stiff, straight, not twisted. Cells in girdle view 

 rectangular. Valve mantles deep, divided from girdle by a small but definite constriction, 

 giving the appearance of lines running around the cell dividing it into three more or less 

 equal zones. Surface of valve flat, oblong-elliptic in outline, margins curved, furnished 

 with a small central spine. Bristles strong, stiff and straight, emanating from the surface 

 of the valve just above the valve mantle. Terminal bristles usually shorter than the 

 others, strongly siliceous, approximating the pervalvar axis. Bristles bearing lines of 

 fine dots and small indefinite spines. Foramina varying considerably in size, somewhat 

 rectangular in shape, usually large. Chromatophores : numerous small rounded bodies 

 penetrating the bristles. Diameter of valve, polar axis 20-46^. 



A very common oceanic species, widely distributed in north polar waters, extending 

 southwards through all European seas. Less frequent in tropical seas, common in south 

 temperate seas, but seldom found in Antarctic waters. The species prefers high salinity. 

 It was found frequently around the coast of South Africa, and South Georgia. 



Observed at Sts. 262, 365, 368, 369, 378, 379, 380, 381, 382, 383, 384, 386, 387, 388, 

 428, 451, 460, 475, 477, 505, 509, 510, 513, 681 ; WS 707. 



Chaetoceros atlanticum var. neapolitana (Schroder) Hustedt. 



Hustedt, 1930, p. 645, fig. 366. 



Chaetoceros neapolitanum Schroder, 1900, p. 29, pi. 1, fig. 4. 



Cells united to form chains, very similar to the type species, but much narrower. 

 Valves almost circular, small central spine present, often seen only with difficulty. 



