REPORT ON THE 1)1 ATOM ACE/E. 125 



Cestodiscus gemmifer, n. sp., var. nov. ^Plate VII. fig. 7.) 



The frustulc here shown can only be regarded as a variety of Cestodiscus gemmifer, 

 n. sp. It differs from the latter (1.) in the character of its granules, which are smaller 

 and are sparsely and irregularly disposed iu the centre, from which they radiate towards 

 the circumference, leaving at first smooth alternating areas between the radii, but becoming 

 crowded more peripherally, and finally diminishing, so as to give a striated appearance 

 to the border ; (2.) in the greater number — forty-eight — of its denticules ; and (3.) in the 

 narrower condition of the border, so that the denticules are placed nearer to the margin. 



Cestodiscus gemmifer, n. sp., var. decrescens, nov. (Plate XII. fig. 11.) 



This variety of the same typical Cestodiscus gemmifer may be distinguished from the 

 latter in the following respects : (1.) The granules are large in the centre, and diminish 

 towards the margin ; and (2.) the periphery is ornamented with a quincuncially disposed 

 granulation, while the outermost belt is very delicately striated. 



Cestodiscus parmula, n. sp. (Plate VII. fig. 5.) 



Valvis rotundis, granulatis ; granuli potiores vel margaritas e centro irregulari radiantes, 

 quandoque spatiis intercedentibus, ad marginem confertse et subito in strias exeuntes ; ad 

 zonam marginalem latam in plures circulos distinctam pauciores spinae vel denticuli 

 distribuuntur. Ad Oceanum Pacificum. 



This frustule is especially distinguished by the extraordinary size of the round granules. 

 The smooth umbilical area is absent, being replaced by one ornamented with a few large 

 granules, and from this radiating granulated lines pass towards the periphery. Between 

 these lines bare spaces may sometimes be observed, while secondary granulated lines 

 become interpolated towards the peripheral ends of the former, and finally the granules 

 become contiguous before passing abruptly into the condition of fine striae. The convexity 

 of the central part of the disc is moderate, and the margin — the inner part of which carries 

 a considerable number of denticules — is broad and divided into several distinct concentric 

 circles. It thus resembles one of the shields x used in warfare by the ancient Romans, a 

 circumstance which has suggested the specific name that has been adopted. 



Cestodiscus (?) rapax, n. sp. (Plate XVIII. fig. 2.) 



Forma rotunda, parva, circum convexa, medio concava ; cellulis aequalibus, medio 

 radiatim, in margine decussatim dispositis ; pluribus (11) apicibus circum radiantibus, et 

 ad instar ungularum assurgentibus. 



This type differs greatly from all the previously mentioned Cestodisci, and its generic 

 determination must for the present remain doubtful. Its form is discoid, its centre con- 



1 Parmula, a small round shield. 



