SYSTEMATIC ACCOUNT 255 



larly disposed over the valve, superimposed as it were, upon the striations. These 

 clusters are very small and give the surface of the valve a denticulate appearance when 

 viewed under low magnification. Connective zone narrow, simple. Chromatophores : 

 numerous small rounded bodies. Type locality, Philippine Islands. Diameter of cell 

 56-64/x. 



This small form has a wide distribution throughout the Indian and Pacific Oceans. 

 It was observed frequently in the Southern Ocean, particularly around Bouvet Island 

 and South Georgia. The specimens exhibited great regularity of size. 



Observed at Sts. 451, 463, 477, 478, 479, 501, 502, 503, 505, 506, 508, 510, 544. 



Genus Ethmodiscus Castracane 

 Castracane, 1886 



Ethmodiscus gazellae (Janisch ex Grunow) Hustedt. 



Hustedt, 1928, p. 375, fig. 196. 



Coscinodiscus gazellae Janisch ex Grunow, 1879, p. 688. 

 Ethmodiscus Wyvilleanus Castracane, 1886, p. 170. 

 Ethmodiscus tympanum Castracane, 1886, p. 170. 

 Ethmodiscus gigas Castracane, 1886, p. 169. 



Cells very large, cylindrical, circular in valve view, subrectangular in girdle view. 

 Valves convex, often deeply so, central area flat, frequently depressed. Valves covered 

 with extremely fine puncta in radial lines; central hyaline area present, area small. 

 Girdle much developed, simple. Diameter of valve 700-1000^; pervalvar axis up to 

 1500^. 



One of the largest known diatoms, somewhat weakly siliceous. It has a restricted dis- 

 tribution in the northern hemisphere, and has been reported from the Mediterranean 

 by Pavillard. Widely distributed in the Southern Ocean, but seldom found in great 

 numbers. An oceanic species favouring cold water. 



Observed at Sts. 508, 510. 



Ethmodiscus subtilis Karsten. 

 Karsten, 1905, p. 87, pi. 8, fig. 3. 



Cells in valve view circular, cylindrical in girdle view. Valves weakly convex, some- 

 times slightly depressed at the centre. Valves covered with fine punctation. Puncta in 

 the centre of the valve arranged in radiating lines, but in the peripheral area the lines 

 appear to be somewhat curved. Central hyaline area and rosette absent. Spinulae ab- 

 sent. Girdle well developed, simple. Chromatophores: several small rounded bodies. 

 Diameter of valve 40^ ; pervalvar axis 54/M. 



A small species having a wide distribution in the Antarctic. Neritic, but often found 

 in deep sea plankton. 



Observed at Sts. 570, 575, 615, 619, 661. 



D XVI 14 



