SYSTEMATIC ACCOUNT 3 , 7 



hollow at the base, and furnished with well-developed basal wings, which envelop the 

 apex of the valve ; wings rounded. Valves bearing depressions which correspond to the 

 spines of sister cells. Connective zone composed of two lines of dorsiventral intercalary 

 scale-like markings. Scales very narrow. Chromatophores : numerous rounded bodies. 

 Diameter of cell, 100-160/x. 



An oceanic species, usually regarded as a warm-water form, found frequently in the 

 Mediterranean. It was observed frequently and sometimes in considerable quantities, 

 in the Drake Strait, particularly around Cape Horn. It occurred far south in the Bel- 

 lingshausen Sea, but not so plentifully as in the Drake Strait. At one station it was 

 observed under tropical conditions, namely St. 1584, off the coast of Somaliland. 



Observed at Sts. 385, 386, 387, 388, 560, 575, 578, 580, 1584; WS 469, 709, 710. 



Rhizosolenia rhombus Karsten. 



Karsten, 1905, p. 97, pi. 10, fig. 6 a-c. 



Cells large, usually solitary, but sometimes in short chains. Cells cylindrical, slightly 

 flattened laterally, almost rhombic in outline. Valves shortly conical, oblique, termin- 

 ated with a short but stout spine. Spine not bulbous, hollow at the base, penetrating 

 the valve. Spine furnished with thin wing-like projections, usually present on both sides 

 of the spine, but more strongly developed upon the ventral side. Connective zone com- 

 posed of two lines of dorsiventral intercalary scale-like markings. Scales narrow. 

 Imbrications usually clear, but seldom parallel. Scales furnished with a fine punctation, 

 usually arranged in quincunx. Chromatophores: numerous cocciform bodies, usually 

 arranged in lines radiating from an eccentric nucleus. Diameter of cells 100-180/x; 

 pervalvar axis 400-500/i. 



Probably a neritic species and typical of the sub-Antarctic zone. It was observed, 

 often in considerable numbers, at a number of stations around South Georgia. 



Observed at Sts. 334, 335, 339, 384, 461, 478, 479, 508. 



Rhizosolenia robusta Norman ex Pritchard. (PI. XI, fig. 13.) 



Norman, in Pritchard, 1861, p. 866, pi. 8, fig. 42. 



Gran, 1905, p. 50, fig. 57. 



Karsten, 1906, p. 163, pi. 29, fig. 10. 



Hustedt, 1929, p. 578, fig. 330. 



Lebour, 1930, p. 94, fig. 68. 



Rliizosolenia sigma Schiitt, 1893, p. 22, fig. 12. 



Cells usually solitary, but sometimes in short chains. Cells cylindrical in connective 

 zone, often flattened laterally, possessing large and deeply conical valves. Cells some- 

 times slightly sigmoid or sublunate. Valves slightly curved and terminated by a small 

 sharp spine. Connective zone composed of numerous annular segments ; segments not 

 complete but form discontinuous intercalary bands, with parallel edges. Connective 

 zone rather strongly siliceous and covered with a minute punctation arranged in 

 quincunx. Valves furnished with a number of lines which proceed from the valve 

 margin toward the apex. Chromatophores: numerous cocciform bodies arranged 



