SYSTEMATIC ACCOUNT 319 



An oceanic species having a wide distribution in European waters, usually con- 

 sidered as a northern form. It was observed, however, sometimes in considerable 

 quantities, off the west coast of Africa, off the coast of Natal and to the south of Mada- 

 gascar, under tropical conditions, in the Drake Strait immediately to the north of the 

 South Shetlands, and off Bouvet Island under sub-Antarctic conditions. It was ob- 

 served also in the Pacific material from the Peru Current. 



Observed at Sts. 275, 300-304, 383, 386, 460, 684, 1373, 1570; WS 647, 700, 703, 704. 



Rhizosolenia simplex Karsten. 



Karsten, 1905, p. 95, pi. 10, fig. 1. 



Cells small, cylindrical, symmetrical about the pervalvar axis. Cells straight, valves 

 deeply conical, terminated by a slender tapering spine. Spine hollow at the base. Con- 

 nective zone composed of numerous small squamose intercalary scale-like markings. 

 Imbrications seen with difficulty, owing to the weakly siliceous nature of the cell. 

 Chromatophores : numerous cocciform bodies, usually arranged along the cell wall in 

 association with the eccentric nucleus. Diameter of cell, 10-26/x ; pervalvar axis 

 200-400/x . 



An oceanic species characteristic of the sub-Antarctic zone, widespread throughout 

 the Southern Ocean. It occurred frequently to the south-west of the Cape of Good 

 Hope, and from the South Sandwich Group to South Georgia and Cape Horn ; it was 

 not found in truly Antarctic waters. 



Observed at Sts. 263, 264, 365, 378, 382, 383, 425, 427, 428, 433, 435, 436, 438, 439, 

 440, 478, 479, 510, 659, 1369; WS 630, 706. 



Rhizosolenia Stolterfothii H. Peragallo. (PI. XI, figs. 7, 8.) 



Peragallo H., 1888, p. 82, pi. 6, fig. 44. 



Gran, 1905, p. 49, fig. 55. 



Karsten, 1906, p. 162, pi. 29, fig. 8. 



Hustedt, 1929, p. 578, fig. 329. 



Lebour, 1930, p. 93, fig. 66. 



Eucampia striata Stolterfoth, 1879, p. 835. 



Pyxilla Stephanos Hensen, 1887, p. 88, pi. 5, fig. 36. 



Cells cylindrical, short, united to form curved chains. Valves flattened, slightly 

 rounded at the edges and furnished with a short sharp marginal spine, which fits into a 

 depression upon the valve of the neighbouring cell. Connective zone composed of 

 numerous annular segments, segments discontinuous. The imbrications are seen with 

 difficulty owing to the weakly siliceous nature of the cell. Cell wall without visible 

 structure. Chromatophores: numerous cocciform bodies, nucleus often close to the 

 ventral wall of the cell. Diameter of cell 20-50/*. 



A neritic species, widely spread throughout northern seas, common in the Mediter- 

 ranean. It was observed off the coast of Natal, but only in small numbers. 



Observed at Sts. 433, 434, 435, 439, 1373. 



