238 DISCOVERY REPORTS 



served, lenticular, hexagonally areolate, irregular, coarse. Numerous spinulae over the 

 entire surface, marginal ones conspicuous. Chromatophores : several small plates. 

 Diameter of valve 15-60^, mostly 44/M ; pervalvar axis mostly 30/x. 



A very variable species, widely distributed throughout Antarctic waters. This 

 organism appears in Karsten (1905) as Thai, antarctica n.sp. No explanation is given 

 for this, and it must be assumed that Karsten was unaware of Comber's paper. 



Observed at Sts. 461, 478, 479, 481, 482, 501, 503, 504, 505, 506, 507, 508, 509, 510, 



5 11 - 5^ 542, 543. 55 2 . 553. 576, 577- 57 8 > 580; WS 469, 474, 481, 545, 580; MS 86. 



Thalassiosira condensata Cleve. (PI. XI, figs. 11, 12.) 



Cleve, 1900a, Bd. xxxiv, p. 22, pi. 8, figs. 12, 13. 

 Hustedt, 1928, p. 332, fig. 169. 

 Gran, 1905, p. 20, fig. 15. 

 Lebour, 1930, p. 63, fig. 35. 



Cells shortly cylindrical, in girdle view rectangular. Valves circular, united to form 

 chains by means of a short thread joining the centres of the valves. Central area of valve 

 slightly depressed, valve without any visible structure with the exception of a small 

 central pore from which is exuded the mucous thread. A single row of spinulae at the 

 margin of the valve, sometimes produced as radiating gelatinous threads. Girdle com- 

 posed of numerous intercalary bands. Chromatophores: numerous small plates. 

 Diameter of valve 28-35/x ; pervalvar axis 20-33/*. 



As the identification of this species is somewhat difficult its distribution is uncertain. 

 It has been recorded from the English Channel and from the coast of Norway. It must 

 be considered as a temperate neritic species favouring a fairly high salinity. In the 

 material examined, it was observed in the Peru Current, and also off the coast of South 

 Africa, north of Cape Town. 



Observed at Sts. 260, 261, 262, 1373 ; WS 703, 705. 



Thalassiosira decipiens (Grunow ex Van Heurck) Jorgensen. (PI. XI, fig. 9.) 



Jorgensen, 1905, p. 96, pi. 6, fig. 3. 



Hustedt, 1928, p. 322, fig. 158. 



Gran, 1905, p. 17, fig. 10. 



Lebour, 1930, p. 58, fig. 30. 



Coscinodiscus decipiens Grunow ex Van Heurck, 1881. 



Thalassiosira gelatinosa Hensen, 1887, p. 87. 



Cells discoid, rectangular. Valves circular, united to form chains by means of a long 

 central mucous thread. Spaces between individual cells usually three or four times the 

 pervalvar distance. Valves slightly convex, furnished with areolate structure in curved 

 lines similar to that of Coscinodiscus excentricus, areoles relatively large in the centre of 

 the valve, decreasing as the peripheral zone is reached. Margin of valve furnished with 

 a ring of strong slightly curved spinulae. Spinulae often produced as long mucous 

 threads. Peripheral zone much deeper than in C. excentricus. Chromatophores: 12-20 

 small irregular plates, usually lying close to the valves. Diameter of valve 12-40/x, 

 mostly 32/u ; pervalvar axis 8-18/x ; intercellular thread 30-80^. 



