REPOKT ON THE DIATOMACE/E. 159 



the frustule has been observed from its zonal side; they have accordingly been provi- 

 sionally assigned to the genus Coscinodiscus, with which there at least exist marked 

 affinities. 



Coscinodiscuslafricanus, Janisch, var. rotunda, nov. (Plate XXIV. fig. 3.) 



The type of which the present frustule is regarded as a variety is represented on 

 plate fix. figs. 24 and 25, of A. Schmidt's Atlas of the Diatomacese. 1 The character of the 

 granulation, which radiates from an excentric point, is the same in both, but the figures 

 given by Schmidt are elliptical, while the valve here shown is round, and bears radiating 

 lines which are not equidistant. These differences, however, cannot be looked upon as of 

 more than varietal significance. 



& 



Coscinodiscus decrescens, n. sp. (Plate XII. fig. 14.) 



Valvis striato-cellulosis ; cellulis grandiusculis a ccntro ad marginem minuentibus ; 

 margine nonnullis punctulis (denticulis) signato. Ad mare Philippinarum. 



This minute disc, from the Philippine Sea, is distinguished by the large hexagonal 

 cellules which are found on its central part, but which decrease in size towards the 

 periphery. The margin is ornamented with a few more salient points which render it 

 more distinct and prominent. 



Coscinodiscus ebulliens, A. S., var. nov. (Plate V. fig. 1.) 



The frustule here delineated is adorned with irregular cellules, which are irregularly 

 distributed, the larger usually occupying a well-marked area about half-way between the 

 centre and the periphery. Although presenting marked affinities with Coscinodiscus 

 ebidliens, A. S., which is shown on plate lxi. figs. 11 and 12 of Schmidt's Atlas, it may 

 be readily distinguished from the latter by the possession of a neatly striated margin, 

 which is not represented in the typical species. 



Coscinodiscus undulatus, n. sp. (Plate VIII. fig. 3.) 



E maximis ; cellulis subradiantibus hexagonis ; valvis concentrice undulatis ; centrum 

 oranulo vel cellula vacat. Diametrum = 390 n. In Oceano Pacifico. 



This superb disc, which measures not less than 390 y". in diameter, is ornamented with 

 large hexagonal cellules, except at the centre, where a small smooth space occurs. Its 

 surface is broadly undulated, so that under the microscope the cellules seem to occur in 

 alternate zones — a circumstance which has suggested the specific name. 



1 In a note appended to the explanation of his figure of the typical species Schmidt says : " Peripherie ellip- 

 tisch, Mitte der Sculptur stets zur Seite geschohen." 



