SYSTEMATIC ACCOUNT 315 



Rhizosolenia delicatula Cleve. 



Cleve, 1900 b, p. 28, fig. 11. 

 Gran, 1905, p. 48, fig. 52. 

 Karsten, 1906, p. 163, pi. 29, fig. 8. 

 Hustedt, 1929, p. 577, fig. 328. 

 Lebour, 1930, p. 91, fig. 63. 



Cells cylindrical, united to form short straight chains. Valves flat, but slightly rounded 

 at the margins, furnished with a short marginal spine which fits into a small depression 

 on the margin of the valve of the neighbouring cell. Connective zone furnished with 

 annular segments seen only with great difficulty. Chromatophores : few large plates, 

 rounded or stellate. Diameter of cells i6-22ju ; pervalvar axis 60/x. 



A neritic species, common around the southern coasts of Europe, and the temperate 

 zone of the Atlantic Ocean. It was observed at one station in the Pacific material from 

 the Peru Current. The distribution of this species is not yet fully known. 



Observed at St. WS 593. 



Rhizosolenia fragilissima Bergon. 



Bergon, 1903, p. 49, pi. 1, figs. 9, 10. 

 Hustedt, 1929, p. 571, fig. 324. 

 Rhizosolenia delicatula Gran, 1902, p. 172. 

 Rhizosolenia delicatula Ostenfeld, 1903, p. 568, fig. 123. 



Cells shortly cylindrical, united to form short, loose, but straight chains. Valves 

 weakly convex, furnished with a short spine placed almost in the centre, which fits into 

 a small depression in the neighbouring cell. In small specimens the valves are rounded 

 and the spine appears to be eccentric. Connective zone composed of numerous annular 

 segments which, because of the weakly siliceous nature of the cell, are seen with great 

 difficulty. Chromatophores : numerous small plates. Diameter of cells 20-40/Lt ; 

 pervalvar axis 50ft. 



A neritic species common around the coasts of Europe. It was observed, sometimes 

 in considerable quantities, around the south coast of Africa. 



Observed at Sts. 425, 427, 428, 433. 



Rhizosolenia hebetata Bailey. 



Bailey, 1856, pi. 1, figs. 18, 19. 



"semispina" phase. 



Rliizosolenia hebetata Bailey, forma semispina (Hensen) Gran, 1905, p. 55, fig. 67 b. 

 Rhizosolenia semispina Hensen, 1887, p. 84, pi. 5, fig. 39. 



Cells cylindrical, valves conical, attenuate, armed with a long spine. Spine straight 

 or slightly curved, possessing an internal cavity. Connective zone furnished with two 

 dorsiventral lines of intercalary scale-like markings, scales somewhat rhombic, but have 

 the appearance of a zigzag line when the cell presents a lateral aspect. The upper portion 

 of the connective zone is often clearly marked with a depression corresponding to the 



