3 i6 DISCOVERY REPORTS 



spine of the neighbouring cell. The cell is very weakly siliceous and the striation upon 

 the connective zone, which is extremely fine, is seen only with great difficulty. Chroma- 

 tophores : numerous cocciform bodies. Diameter of cell 5-40/x ; pervalvar axis 400-750/x . 



One of the most common forms of Rhizosolenia observed in the Discovery material. 

 It was observed in all types of water, but more frequently in the waters of the tropical 

 and subtropical zones. It occurred around the coast of Africa, particularly on the west 

 side, but was not frequent around the Cape of Good Hope, and was absent from the 

 material obtained from the eastern side, in the Indian Ocean. It occurred frequently at 

 many stations around South Georgia, the South Sandwich Group, Cape Horn, and far 

 south into the Weddell and Bellingshausen Seas. It was common at many stations in the 

 Peru current and sometimes found in great quantities. Great variation was observed in 

 this species, particularly with regard to dimensions. Many of the specimens from the 

 more southerly stations were very thin, while those from the Pacific side of South 

 America were strong and possessed a much greater diameter. 



Observed at Sts. 289, 292-294, 301, 3°3-3°5. 3 6 5> 3 68 > 3 6 9> 3 Sl . 3 8 3> 3 8 4> 449-45 1 . 

 460, 480-482, 501-506, 508-511, 659, 661, 722; WS 107, 540-543, 545, 547-552A, 

 598, 641, 643, 700, 701, 703-708, 710, 7i4-7 l6 - 



Rhizosolenia imbricata Brightwell. 



Brightwell, 1858, p. 95, pi. 5, fig. 6. 

 Karsten, 1905, p. 98, pi. 11, fig. 3. 

 Hustedt, 1929, p. 580, fig. 331. 

 Rhizosolenia striata Greville, 1866 a, p. 234. 



Cells large, cylindrical, slightly flattened laterally, furnished with shortly conical, 

 strongly eccentric valves, having a strongly oblique ventral side. Valve furnished with a 

 strong marginal spine which appears as a continuation of the dorsal side of the cell, 

 spine straight. Cells often united to form short chains. Connective zone furnished with 

 two lateral lines of intercalary scale-like markings. The markings are regular, with 

 parallel sides, which give the appearance of annular segments with oblique ends. The 

 imbricate scales of the connective zone are strongly marked with lines of areolation 

 arranged obliquely, converging upon a line which occupies a median position on the 

 connective zone, arranged laterally in the transapical plane. Chromatophores : several 

 small rounded bodies. Diameter of cell 80-1 00/x ; pervalvar axis 400-600^. 



An oceanic species having a distribution in tropical and subtropical seas, seldom found 

 in north European waters, but has been observed in the Mediterranean. It was observed 

 at one station only to the south-east of the Cape of Good Hope. 



Observed at St. 443. 



Rhizosolenia polydactyla Castracane. 

 Castracane, 1886, p. 71. 

 Cells cylindrical, often slightly flattened laterally. Valves shortly conical, eccentric, 

 oblique, ventral surface slightly curved. Valves terminated by a short, sharp spine, 



