SYSTEMATIC ACCOUNT 297 



Cells united to form chains. Valves elliptical in outline. Bristles emerge well inside 

 the valve margin and proceed at right angles to the chain axis for a short distance, then 

 sweep downwards converging slightly towards the posterior end of the chain. Neigh- 

 bouring cells seem to coalesce at the point where the bristles emerge causing the 

 foramina to have a rectangular appearance. Valve mantle deep, constricted as it meets 

 the connective zone. Girdle deep, usually twice as deep as the valve mantle. Bristles 

 armed with fine spines. Chromatophores : numerous small oval bodies extending into 

 the bristles. Diameter of valve, polar axis 20-30/* ; pervalvar axis 36-70/x. 



A tropical and subtropical form, fairly common in the Indian Ocean. It was observed 

 occasionally off the coast of South Africa. 



Observed at Sts. 425, 433, 440. 



Chaetoceros sumatranum Karsten. 



Karsten, 1907, p. 388, pi. 45, fig. 2. 

 Ikari, 1928, p. 251, fig. 6. 



Cells united to form short chains, usually four to ten cells in a chain. Cells somewhat 

 cylindrical, valves almost circular, valve surface slightly concave. Bristles long, emerging 

 well inside the valve margin, and proceeding obliquely in almost straight lines, seldom 

 if ever converging towards the axis of the chain. Bristles armed with small spines. Valve 

 mantle deep, slightly constricted as it meets the connective zone. Girdle also deep. 

 Foramina small, narrowly elliptical. Chromatophores: numerous vermiform bodies. 

 Diameter of valve 30-36/x; pervalvar axis 100-120/x. 



A large tropical and subtropical form, common in the Indian Ocean. It was observed 

 at one station only off South Africa. 



Observed at St. 425. 



Chaetoceros Chunii Karsten. 



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



Cells small, united to form short chains. Valves elliptical, valve surface slightly con- 

 cave. Angles produced to form long thin bristles. Bristles straight and smooth. All 

 bristles bent towards the posterior end of the chain. The bristles upon the lower valve 

 of each cell form a more acute angle than do those of the upper valve. Valve mantle 

 deep, constricted towards the connective zone, girdle narrow. Foramina small, elliptic- 

 oval. Chromatophores: numerous small bodies, penetrating the bristles. Diameter of 

 valve 12-15/x. 



A small neritic species, very common in the Antarctic, seldom found N. of 40 S. 

 It was observed very frequently around South Georgia, Cape Horn, South Shetlands 

 and in the Bellingshausen Sea. 



Observed at Sts. 378, 379, 380, 382, 478, 479, 480, 481, 482, 501, 506, 508, 574; 

 WS 104, 545. 



Chaetoceros radiculum Castracane. 



Castracane, 1886, p. 79. 



Karsten, 1905, p. 117, pi. 15, fig. 3. 



19-2 



