Greville^ on New Diatoms. 
75 
Hab. Barbadoes deposit,, from Cambridge estate^ commu- 
nicated by C. Johnson^ Esq. 
This is one of those anomalous forms which disturb the 
natural habit of genera. In A. Ralfsianus we have a similar 
instance^ but in that case the indications of converging 
lines could be perceived by an attentive observer in the 
direction of the puncta within the meshes of the network. 
Here, however, we have a very minute cellulation covering 
the entire valve (with the exception of the processes), without 
any indication of converging lines at all. At the same time 
the diatom is evidently an Auliscus, the processes being un- 
mistakable, and, as in all the other non-circular species, they 
are placed, not in the exact line of the longest diameter, but 
on each side of it. I have examined two specimens and the 
fragment of a third, all of which are precisely alike. 
Triceratium. 
Triceratium lineatum, n. sp., Grev. — Valve with a dense, 
obscurely radiating structure, nearly straight sides, subacute 
angles, and prominent pseudo-nodules; within each angle 
three remote lines, sub-concentric with the angles. Distance 
between the angles about •0040". (Fig. 24.) 
Hab. Barbadoes deposit, from Cambridge estate; C. John- 
son, Esq. 
One of the most distinct species in the whole genus. The 
remarkable lines within each angle include the greater part 
of the surface. The structure is more or less opaque, ex- 
hibiting an obscure radiation in the centre and an exceed- 
ingly fine striation between the curved lines. The pseudo- 
nodules are not large, but very conspicuous. 
Peponia, nov. gen., Grev. 
Valves sub-circular, conspicuously cellulate, suddenly con- 
tracted, above and below, into a triangular apiculus ; cellules 
round. 
The definition of this genus must be regarded as provi- 
sional until the front view of the frustules can be obtained. 
Of the valve I have seen a very considerable number of speci- 
mens, and in several instances the opposite valve partially 
displaced, as shown in the figure, which shows that the con- 
necting zone must be narrow. The apiculus has sometimes 
a distinct appearance of being furnished with a nodule or 
short process, but I have not been able to satisfy myself on 
