SYSTEMATIC ACCOUNT 245 



Sandwich Group and in the Bransfield Strait, sometimes in great numbers. It has been 

 recorded from around the Cape of Good Hope, but is seldom met with north of latitude 

 40 S. A neritic diatom favouring cold water with fairly high salinity. It has not been 

 recorded from the northern hemisphere. 



Observed at Sts. 463, 475, 478, 509, 542, 544, 551, 664; WS 481. 



Coscinodiscus centralis Ehrenberg. 



Ehrenberg, 1839, p. 129. 



Gran, 1905, p. 33, fig. 33. 



Lebour, 1930, p. 39, figs. 16-18. 



Coscinodiscus asteromphalus var. centralis Grunow, 1884, p. 79. 



Coscinodiscus oculus-Iridis var. tenuistriata Grunow, 1884, p. 77. 



Cells discoid, valves gently convex. Valves covered with radial areolation. Central 

 rosette distinct, sometimes strongly marked, the areoles decreasing in size as they pro- 

 ceed to the periphery. Margin of valve furnished with a row of small spinulae, five to 

 six areoles between each spinule. Margin also furnished with two small apiculi, usually 

 situated at an angle of 90-95 . Girdle usually narrow, composed of several intercalary 

 bands. Chromatophores : numerous small plates. Diameter of valve 160-210^, mostly 

 200/i ; pervalvar axis 50-60/^. 



A temperate species with a world-wide distribution, very common around South 

 Georgia in the spring and summer. Generally regarded as an oceanic species. 



Observed at Sts. 507, 670, 719, 721 ; WS 647; MS 86, 88, 89, 90, 92, 94, 95, 97, 98, 

 99, 100, 101, 102, 103. 



Coscinodiscus concinnus Wm Smith. 



Smith, 1856, p. 85. 

 Lebour, 1930, p. 43, fig. 19. 

 Hustedt, 1928, p. 441, figs. 241, 242. 



Cells large, circular in valve view, almost rectangular in girdle view. Valve slightly 

 convex, often slightly flattened at the centre. Valve surface covered with very fine 

 areolation. Central rosette large, but often inconspicuous, the areolae decreasing in 

 size as they proceed to the margin. Margin of valve furnished with fine spinulae, from 

 which hyaline ribs or lines proceed to the centre of the valve. Two small but distinct 

 apicules are situated asymmetrically on the valve margin. The pervalvar axis is often 

 equal to the diameter of the valve and the girdle is composed of numerous intercalary 

 bands. A weakly siliceous diatom, which collapses on drying. Chromatophores: 

 numerous small rounded bodies. Diameter of valve 380-465/u., mostly 460^ ; pervalvar 

 axis usually 440^. 



A neritic diatom, common in temperate and subtropical seas. 



Observed at Sts. 1373, 1 575. 



Coscinodiscus decrescens Grunow in Schmidt. 



Grunow (in A. Schmidt's Atlas) (1878) pi. 61, figs. 7-10. 

 Karsten, 1905, p. 87, pi. 8, fig. 1. 

 Hustedt, 1928, p. 430, fig. 233. 



