42 THE VOYAGE OF ELMS. CHALLENGER. 



According to Arnott, the difference between Gephyria and Eupleuria consists in the 

 fact that in the latter the zonal side is formed of rings of short septa while the margins 

 are beaded, whereas in the former the connecting zone is sublamellate and finely striated on 

 the surface. 1 Since, however, it is true that the shape and structure of the two types are 

 essentially identical, they must be regarded as being generically equivalent, although the 

 EupleuricB may be considered as a distinct section of the Gephyrice. 



Gephyria gigantea, Grev. (Plate XV. fig. 10.) 



This figure represents a magnificent Gephyrian valve from the neighbourhood of 

 Kerguelen Island, where numerous interesting Diatoms have been found. It reminds 

 the observer of Gephyria gigantea, Grev., which is shown on plate xi. figs. 7 and 8 of the 

 Transactions of the Microscopical Society of London, vol. xiv., new series, 1866. Eugenie 

 O'Meara also describes 2 and figures under the name of Gephyria dyerana, in his work on 

 the diatomaceous gatherings made at Kerguelen Island by the Expedition, a form 

 of valve which seems to be identical with that recognised by me from the same spot and 

 very probably from the same collection. 



On comparing the three figures above referred to as well as the descriptions given by 

 O'Meara and Greville, no difference is apparent except the circumstance recorded by the 

 former, that the valves are flat in the centre and arched at the extremities. This, however, 

 cannot by itself be regarded as a good foundation on which to establish a new species, so 

 that the form shown on our Plate XV. fiw. 10 must be regarded as identical with that 

 described and figured by O'Meara. Moreover, as no distinction is apparent between the 

 latter and the Grevillean type, the designation adopted by the last-named author should 

 be selected on account of its priority. 



Gephyria, n. sp. (?) (Plate XXV. fig. 19.) 



We have here a representation of the superior valve of a very small Gephyrian 

 frustule, marked by transversely disposed costules which alternate on the two sides. The 

 two halves of the valve are separated by an undulating central line. 



It is indeed true that similar characteristics are seen on the valve of Eupleuria, and 

 particularly on the superior valve — a circumstance which goes to justify the reunion of 

 the two genera Gephyria and Eupleuria into one — but since the two valves of the genus 

 are constantly dissimilar, and since, in the present case, the characteristics of the con- 

 necting zone are unknown, it may in the meantime be indicated as probably a new species 

 of Gephyria, although its true specific or non-specific value can be determined only when 

 its characters are more fully known. This frustule was gathered at the port of Tahiti. 



1 Quart. Journ. Micr. Sci, voL viii. p. 20. 



2 Journ. Linn. Soc. Lond. (Botany), vol. xv. p. 59, pi. i. fig. 10. 



