SYSTEMATIC ACCOUNT 305 



minal cell are usually small and somewhat tortuous. Foramina somewhat hexagonal, 

 merging to circular. Chromatophores : solitary, adpressed to the connective zone. 

 Diameter of valve in the polar axis 12-46^, mostly 36/x. 



A tropical and subtropical oceanic species, frequent in the Indian and Pacific Oceans, 

 seldom in the Atlantic. Very common off the coast of South Africa. 



Observed at Sts. 425, 427, 428, 429, 433, 434, 435, 43 6 - 437- 438. 439, 440, 1373; 

 WS 630, 631, 641. 



Section Curviseta 

 Chaetoceros debile Cleve. 



Cleve, 1894, 20, p. 13, pi. 1, fig. 2. 

 Gran, 1905, p. 92, fig. 117. 

 Hustedt, 1930, p. 740, fig. 428. 

 Lebour, 1930, p. 158, fig. 121. 

 Chaetoceros vermiculus Schutt, 1895, p. 39. 



Cells united to form long curved and often twisted chains. Cells rectangular in girdle 

 view, often square, oval in valve view. Valves flat or weakly convex. Bristles thin, 

 emanating from the corners of the cell. Bristles curved and all bent towards the same 

 side of the chain, giving to the chain the appearance that all the bristles emerge from one 

 side of the cell only. Foramina, narrowly oblong. Chromatophores : one large plate. 

 Diameter of valve in the polar axis 18-34^. 



A neritic species, common around all European coasts. Observed at one station only 

 off the Falkland Islands. 



Observed at St. WS 100. 



Chaetoceros sociale Lauder. 



Section Socialia 



Lauder, 1864, p. 77, pi. 8, fig. 1. 

 Gran, 1905, p. 96, fig. 123. 

 Hustedt, 1930, p. 751, fig. 435. 

 Lebour, 1930, p. 166, fig. 128. 



Cells united in curved chains, held together in large rounded gelatinous colonies. 

 Cells rectangular in girdle view, oval in valve view, valve surface flat. Bristles very fine, 

 crossing those of the neighbouring cells outside the girdle line. Bristles of unequal 

 length. Foramina, narrow, hexagonal. Chromatophore: one small plate. Diameter of 

 valve in the polar axis 8-12^. 



A neritic species having a wide distribution from temperate to almost subpolar seas, 

 common in north Atlantic waters. It was observed very frequently around South 

 Georgia, off the Falkland Islands and throughout the Southern Ocean generally. It was 

 noticed that the amount of mucilage required by the colonies increased as the species 

 proceeded southward. 



Observed at Sts. 378, 379, 380, 382, 479, 480, 482, 502, 505, 507-513 ; WS 100, 101, 

 580, 647, 700. 



