8 
Greville^ on New Diatoms. 
with the specific character adopted by Mr. Ralfs [' Pritch. 
Inf./) ; but a slight convexity is very different from the 
prominent gibbous curve in the valve now before me. The 
presence of strong spines also_, by themselves of very uncer- 
tain value,, contributes, in connection with the other charac- 
ters, to confer upon it great prima facie distinctness. Size 
alone is of little importance, but it may be well to state that 
it is scarcely more than half that of T. Favus, as figured in 
the ' Synopsis of British Diatomacese.^ At the same time the 
margin is far more decidedly defined, and the reticulation 
more delicate. After all, however, it may turn out to be 
nothing more than an extreme form of T. Favus, to which 
Mr. Ralfs seems disposed to refer T. grande of Brightwell. 
Triceratium Stokesianum, n. sp., Grev. — Large ; valve with 
slightly concave sides and subobtuse angles; surface with 
subremote, roundish, irregularly radiating cellules, minute 
in the centre, becoming large towards the sides and angles ; 
angles imperfectly cut off by two vein-like lines springing 
from the margin on each side, obscurely united in the middle ; 
margin strong, remotely striate. Distance between the 
angles -0062". (Fig. 23.) 
Hab. Moron deposit. Province of Seville; Rev. T. G. 
Stokes ; extremely rare. 
This fine species appears to be allied, as my kind corre- 
spondent Mr. Stokes remarks, to T. areolatum of the Bar- 
badoes deposit, being of the same form, and having a very 
similar radiating cellulation ; but it differs in being a very 
much larger species, and in having the angles partially cut off 
by a pair of vein-like undulating lines given off on each side, 
which become faint and obscure towards the middle. The 
pair next the angle are less distinct than the others, and 
would probably be found obsolete in some specimens. The 
cellules are sometimes oval, and are larger and more regular 
as they approach the angles. The Moron deposit is remark- 
able for the small number of individuals of the new species 
which have been found in it. No one but Mr. Stokes has 
been so fortunate as to discover the subject of the present 
notice. 
Triceratium Inelegans, n. sp., Grev. — Small ; valve pulvi- 
nate, with straight sides and broadly rounded angles ; 
whole surface filled with irregularly radiating, somewhat 
remote, oblong, rather large granules, except the angles, 
which are minutely punctate. Distance between the angles 
•0025". (Fig. 21.) 
Triceratium obtusum ? Ehr., ^ Mikrog.^ Tab. xviii, 
fig. 48. 
