20 THE VOYAGE OF H.M.S. CHALLENGER. 



Amphora staurophora, n. sp. (Plate XXVII. fig. 6.) 



Valvis cymbiformibus, apicibus acutis ; linea ventrali subrecta, dorsali convexa ; 

 nodulo medio in staurum ad margineni dilatato. Ad portum Thaiti. 



The narrow stauros of this little cymbiform valve extends to the margin. The dorsal 

 line is convex and presents a slight constriction at its junction with the stauros. The 

 ventral line is straight, and the extremities are slightly inflexed. The apices of the 

 valve are acutely rounded. The striation is very delicate and transverse. 



The specific name has been derived from its long and well-defined stauros. 



Amphora oceanica, n. sp. (Plate XXVII. fig. 20.) 



Valvis deorsum subinflatis, introrsum late concavis; apicibus obtusisrotundatis; nodulo 

 centrali lineam marginalem subattingente ; striis tenuissimis transversis. Prope Sydney. 



This new form, from the waters near Sydney, appears at first sight to be a variety of 

 Amphora obtusa, 1 Greg., but to regard it thus would widen the limit of that species to 

 too great an extent, so that the two forms cannot be included in the same category. 



In Amphora oceanica the terminal nodules are not distinct, and the central nodule is 

 in close proximity to the internal profile of the valve. The striation is singularly delicate 

 and, as in Amphora obtusa, Greg., transverse. 



Cymbella, Ag. Kg. 



Two of the frustules described under this genus, and represented on Plate XXVII. figs. 

 5 and 13, namely, Cymbella criophila from the south of Heard Island, and Cymbella 

 marina from the neighbourhood of Yedo, Japan, seem, at first sight, to belong to the 

 genus Amphora. Since, however, the characteristic of that genus is to have a central 

 marginal nodule, they cannot be included in that group, but must be classed as Cymbella, 

 although no members belonging to the latter genus have been hitherto recorded as marine. 



That an admixture of fresh-water and salt-water Diatoms should occur in marine 

 gatherings is to be expected, however, when it is borne in mind that frustules of the 

 former must often be carried into the sea by rivers. Thus Asterionella formosa, 2 Hass., 

 and Eunotia arcus, 3 Ehrenb., which, like all other Eunotice, vegetates at an elevation of 

 several hundred feet above the level of the sea, have been detected in sea water ; yet it 

 cannot be doubted that Cymbella marina is a true pelagic form, and it is probable that 

 Cymbella criophila has the same habitat. That representatives of this genus do live 

 normally in sea water has indeed been clearly proved by me while working in the 



1 Micr. Journ., vol. v. pi. i. fig. 34. 



2 Micr. Journ., vol. viii. pi. vii. fig. 8 ; Microscopical Examination of the Water supplied to the Inhabitants 

 of London, by Mr. Hassall, p. 10; Smith, Synopsis of the British Liatomacese, vol. ii. p. 81. 



3 Abhandl. d. k. Akad. d. Wiss. Berlin, 1840, p. 17 ; Rabenhorst, Siissw. Diat., fig. 6; Wigand in Hedwigia, 

 vol. ii. p. 43, pi. vii. figs. 13 and 14. 



