2 4 o DISCOVERY REPORTS 



Hustedt, 1928, p. 330, fig. 166. 



Lebour, 1930, p. 64, fig. 36. 



Podosira subtilis Ostenfeld ex Ostenfeld et Knudsen (1899), p. 55. 



Cells discoid, small, colonial, usually embedded in a gelatinous mass. Valves circular, 

 convex. Girdle composed of annular segments. The surface of the valve is almost with- 

 out structure, with the exception of a few extremely fine and isolated granules in the 

 centre ; at the margin is a ring of very small spinulae and one apicule. Chromatophores : 

 eight to ten small plates. Diameter of valve 20-30/x; pervalvar axis 10-15/*. 



An oceanic species very common in the Atlantic and Southern Oceans, sometimes 

 found free, but mostly in enormous colonies embedded in a gelatinous film, very com- 

 monly mixed with Corethron. In the more southerly and colder waters the production 

 of the gelatinous film was more frequent than in warmer waters. 



Observed at Sts. 381, 434, 435, 436, 437, 438, 439, 512, 1373 ; WS 645, 705, 706, 709, 

 710, 711, 712, 713, 714. 



Genus Lauderia Cleve 

 Cleve, 1873 

 Lauderia borealis Gran. 



Gran, 1900a, p. no, pi. 9, figs. 5-9. 

 Hustedt, 1929, p. 549, fig. 313. 

 Lebour, 1930, p. 66, fig. 38. 



Cells shortly cylindrical, irregularly rectangular in girdle view. Valves circular, 

 united to form short chains. Cells weakly siliceous, valves slightly convex, with slight 

 depressions in their centres. The margin of the valve is furnished with a number of 

 extremely fine spines, which are visible only if the specimens are examined when 

 mounted dry ; an indistinct apicule is also present. Peripheral zone of valve covered 

 with fine areolate punctation. Girdle composed of annular segments, which as a rule 

 are seen only when the specimen is mounted dry. Chromatophores : numerous small 

 irregularly rectangular plates. Diameter of valve 40-48/1; pervalvar axis 45 /x. 



An oceanic diatom which favours warm water of a high salinity : common in Indian 

 Ocean, it has been reported from the Mediterranean, but seldom is found in the 

 northern hemisphere. 



Observed at St. 1373. 



Lauderia punctata Karsten. 



Karsten, 1907, p. 374, pi. 42, fig. 7. 



Cells cylindrical, usually three times longer than broad, united by mucous threads to 

 form straight chains. Valves circular, almost touching each other, having a median 

 depression, and rounded margin. Margin furnished with spinulae. Girdle composed 

 of annular segments, bearing moniliform striation, puncta arranged in quincunx. 

 Chromatophores : numerous vermiform bodies. Diameter of valve 20-34/x, mostly 30/1 ; 

 pervalvar axis mostly 90/1. 



This species was observed off the coast of South Africa and in the Peru Current off 



