82 Greville, on New Diatoms. 



sideSj rounded angles^ double pseudo-nodules, and simple 

 margin ; centre a triangular space, filled with radiating moni- 

 liform lines ; border divided by transverse lines into punctated 

 compartments. Distance between the angles, about '0026". 

 (Fig. 5.) 



Triceratium marginatum, Brightw., ^Mic. Journ./ vol. iv, 

 p. 275, pi. xvi, fig. 13. Ralfs, in 'Pritch. Infus./ 1861, 

 p. 854. 



Hah. Barbadoes deposit, chiefly from Cambridge Estate ; 

 extremely rare; T. Brightwell, Esq., F. Kitton, Esq., Dr. 

 Greville. 



Although this fine species has been, in all essential points, 

 correctly figured in Mr. Brightwell's paper quoted above, I 

 have a twofold purpose in introducing another illustration in 

 this place. It is very desirable that the student should be 

 able at once to compare with it the new and allied species I 

 am about to describe, most of which I have received under 

 the same name. I wish, besides, to represent a sti'uctural 

 arrangement which does not appear iu Mr. Brightwell's 

 figure. This consists of a circular, blank space surrounding 

 the apex of the angle of the inner triangle and the inferior 

 pseudo-nodule. It contains no puncta ; and several faint, 

 short lines, and two dark and longer ones, radiate from it. 

 It is probable that this character may be more or less obscure 

 in some individuals, as it is by no means conspicuous in 

 Mr. Kitton's specimen, which he has kindly permitted me to 

 examine. It would appear that no dependence can be placed 

 on the number of lateral costse. In INIr. Kitton's example 

 there are two on each of two sides, and three on the other. 

 In my own the number on two sides is similar, but there is 

 only one on the third side. INIr. BrightwelFs figure shows 

 four on each of two sides and three on the other. With 

 regard to the radiating lines of the inner triangle, I am in- 

 clined to consider them as modified costse. Much depends 

 upon the angle at which they are viewed. In my own 

 specimen they have all the appearance of lines of puncta, 

 but in Mr. Kitton's valve the costate character comes clearly 

 out, with the addition of being nodulose, especially as the 

 costse approach the margin of the inner triangle. 



Triceratium pulcherrimum , n. sp., Grev. — Valve with 

 slightly convex sides, rounded angles, and simple margin; 

 centre a triangular space, filled with radiating costse ; border 

 divided by transverse lines into punctated compartments, 

 which are continued round the large, oblong pseudo-nodules. 

 Distance between the angles '0045". (Fig. 6.) 



Hab. Barbadoes deposit, C. Johnson, Esq. ; exceedingly 

 rare. 



