82 
GrevillEj on New Diatoms. 
sides_, 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. 
Hab. 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 ]\Ir. BrightwelFs 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 structural 
arrangement which does not appear in Mr. BrightwelPs 
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 Mr. 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. Mr. BrightwelPs 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, 
bat in Mr. Kitton^s valve the costate character comes clearly 
out, with the addition of being noduh)se, 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''. (Eig. 6.) 
Hab. Barbadoes deposit, C. Johnson, Esq.; exceedingly 
rare. 
