KErORT OX THE IUAToMACE.E. 49 



Rhaphoneis elliptica, n. sp. (Plate XXVI. fig. 13.) 



Parva, elliptica, duplo longior quam latior ; costis crebriusculis radiantibus, area 

 lineari lauceolata medio interruptis. Ad mare Japonicum. 



This small elliptical Diatom is twice as long as broad. Its costules, which radiate like 

 those of Rhaphoneis mammalis, n. sp., are more closely arranged, and more prominent than 

 in the latter frustule. 



The smallness of its size, and the absence of granulated striae, distinguish it from the 

 Rhaphoneis fasciolata of Ehrenberg, 1 but it bears some resemblance to the lower valve 

 of a Cocconeis. Since, however, no upper valve belonging to this genus was observed 

 in the rich collection, and since the smooth central space characteristic of the genus 

 Rhaphoneis is present, it has from its shape been named Rhaphoneis elliptica. It was 

 gathered in the Sea of Japan. 



Rhaphoneis japonica, n. sp. (Plate XIX. fig. 12.) 



Mediocris, elliptica ; apicibus cuneato rotundatis ; distinctiorum granulorum lineis 

 subradiantibus ; granulis circum regulariter stipatis, medio irregulariter rarioribus. In 

 mari Japonico. 



The determination of this species has been a work of no small difficulty. In it no 

 trace of a smooth area or of a median longitudinal line is to be found, so that, although 

 apparently not a Rhaphoneis, no other genus exists to which it could be more readily 

 ascribed. On consulting the various writers on Diatoms, and comparing their figures 

 with the present type, an oblong, elliptical form — different, indeed, from the form now in 

 question, but evidently belonging to the same genus, — which resembles the Rhaphoneis 

 australis of H. L. Smith, is represented at fig. 54 given in a paper on the "Diatoms 

 collected during the Expedition of the Vega," by P. T. Cleve, under the name of 

 Trachisphenia australis. 



In order to understand how a form that presents no trace of central division can be 

 called a Rhaphoneis, reference may be made to the Synopsis of the families and genera of 

 Diatoms by H. L. Smith, as given at the end of Dr Van Heurck's work on the Microscope 2 

 (third edition), where, in the definition of the genus, after having said, " ayant une ligne 

 mediane ou un espace blanc," he parenthetically adds, "souvent obscur ou manquant," so 

 that amongst the characteristics of a genus the essential should always be distinguished 

 from the less essential features. 



Since, however, this frustule from the Sea of Japan cannot be confounded with 

 Rhaphoneis australis, H. L. Sm., as it differs both in form and in the character of its 

 granulation, it must be regarded as a new species, and has been named from the locality 

 in which it was found. 



1 Mikrogeol., T. xxxv. A. 22, fig. 16. 



2 Le Microscope, sa Construction, son Mainement, et son Application a l'anatomie Vegetale et aux Diatonie'es 

 (troisieme Edition), Bruxelles, 1878. 



(bot, chall. ezp. — part iv. — 1886.) D 7 



