SYSTEMATIC ACCOUNT 301 



Section Protuberantia 



Chaetoceros didymum Ehrenberg. 



Ehrenberg, 1845, p. 75. 

 Gran, 1905, p. 79, fig. 94. 

 Karsten, 1906, p. 168, pi. 32, fig. 11. 

 Lebour, 1930, p. 133, fig. 97. 



Cells united to form straight chains. Valves elliptical in outline, surface slightly con- 

 cave with a very prominent semicircular median inflation or knob. Angles of the valves 

 very slightly produced, giving rise to the bristles, which meet those of the neighbouring 

 cell usually a very short distance beyond the valve margin. Bristles often curved, those 

 of the terminal cell are usually a little stouter than the others, and bear very small spines. 

 A very variable species. Chromatophores : two large plates, lying close to the valves. 

 Foramina varying considerably in shape, usually elliptical, sometimes broadly oval, 

 penetrated on the upper and lower sides by the mammiform processes upon the 

 opposing valve surfaces. Diameter of valve, polar axis 10-48/x. 



A neritic species widely distributed in temperate seas. It was observed frequently 

 around the coast of South Africa, and in the Pacific material from the Peru Current. 



Observed at Sts. 260, 262, 425, 427, 428, 433, 434, 435, 437, 438, 507; WS 700, 710, 



7H> 7 r 5- 



Section Laciniosa 



Chaetoceros laciniosum Schiitt. 



Schiitt, 1895, p. 38, fig. 5. 

 Gran, 1905, p. 82, fig. 99. 

 Meunier, 1910, p. 235, pi. 26, fig. 24. 

 Hustedt, 1930, p. 701, fig. 401. 

 Lebour, 1930, p. 137, fig. 100. 



Cells united to form straight chains, usually four to twelve cells in a chain. Cells in 

 girdle view rectangular, angles rounded. Valves elliptical in outline, slightly convex. 

 Bristles emerging from the apices of the valve, proceeding upwards parallel with the 

 chain axis to meet those of the neighbouring cell, which are crossed in line with the 

 margin of the valve, and then turn outwards in sweeping curves. The bristles of the 

 lower valve of a terminal cell are often bent as they emerge from the cell, causing them 

 to cross, or to converge considerably. These terminal bristles are much longer and 

 stouter than the others and are armed with short spines. Foramina rectangular. 

 Chromatophores: two large plates, adpressed to the valves. Diameter of valve, polar 

 axis 30-38^. 



A neritic species having a wide distribution in the north Atlantic and north European 

 seas. It was observed at one station only on the 30th W meridian. 



Observed at St. 666. 



