332 DISCOVERY REPORTS 



Fritsch (1912, p. 49) and Carlson (1913, p. 31) placed Fragilaria antarctica into the 

 genus Denticida Kutzing. This is to misunderstand entirely the structure of Denticala, 

 for that genus possesses a prominent canal-raphe and intercellular craticular structures, 

 neither of which is present in Fragilariopsis. Heiden and Kolbe (1928) added to 

 Fragilariopsis two species previously described by Van Heurck (1909) as species of 

 Fragilaria. 



Fragilariopsis antarctica (Castracane) Hustedt in Schmidt. (PI. XIII, figs. 11, 12.) 



Hustedt, in Schmidt, 1913, pi. 299, figs. 9-14. 

 Fragilaria antarctica Castracane. 

 Castracane, 1886, p. 56, pi. 25, fig. 12. 

 Karsten, 1905, p. 122, pi. 17, fig. 7. 



Cells sometimes single, but usually united to form long ribbon-like chains. Chains 

 straight. Valves slightly convex, sometimes flat, elliptic-lanceolate in outline, apices 

 rounded. Valve-surface furnished with two systems of markings. The main structure of 

 the valve consists of a grill or framework, in the form of several, usually five to thirty, 

 stout bars, arranged transapically, which connect with a strong marginal valve-rim. 

 Between the transverse bars, and upon a lower plate, are numerous puncta, usually 

 arranged in two parallel lines. The connective zone is narrow and simple. The cell is 

 strongly siliceous, and from examinations of deep-sea muds made in the neighbourhood 

 of Tristan d'Acunha, it is evident that an enormous bed of diatomaceous earth is in the 

 process of formation, which consists very largely of the frustules of this species. 

 Chromatophores : two elongated plates, lying close to the valves, nucleus central. 

 Transapical axis 6-14/x ; apical axis 20-80/A. 



One of the most common Antarctic diatoms, often found in enormous quantities, 

 probably oceanic. It is liable to considerable variation in size and shape, and in the 

 number of transverse bars upon the valve surface. 



Observed at Sts. 300-302, 365, 368, 378-386, 388, 451-453, 460, 461, 463, 475, 

 477-482, 501, 504-508, 511-513, 542, 544, 552, 560, 570, 574, 575, 577, 578, 617, 659, 

 661, 666, 670, 1356, 1359, 1362, 1369; WS469, 474, 481, 541, 542, 543, 545, 547- 

 552 a; RS9. 



"bouvet" phase. 



Fragilaria antarctica, forma bouvet Karsten, 1905, p. 123, pi. 17, fig. 10. 



This is very similar to the type phase, and is found associating with it. It differs in 

 possessing a more regularly rectangular girdle view, so that the cells lie closely ad- 

 pressed throughout the whole of their length when in chain formation. The markings 

 upon the cell are usually less vigorous, the chromatophores usually smaller, and the cells 

 show greater regularity in size and shape. Transapical axis 8-14/^, apical axis 20-40^. 

 Probably a neritic phase. 



Observed at Sts. 460, 461, 576, 577, 615, 617, 619; WS 481. 



