92 
GrevillEj on New Diatoms. 
obvious radiating arrangement in the minutely punctate 
structure. 
Triceratium perpusillum, n. sp., Grev. — Minute ; valve with 
the sides very deeply concave, and the angles broadly rounded; 
centre smooth^ the angles filled with an oval mass of very 
minute puncta. Distance between the angles 'OOIS'". (Fig. 
13.) 
Hab. Barbadoes deposit^ Cambridge estate; in slides 
communicated by C. Johnson, Esq. 
In this minute and well-marked species I cannot per- 
ceive that the angles are cut off from the centre by a 
transverse line. It is not therefore so closely allied to 
T. castellatum and Normanianum, as it would appear to be 
from its form. 
Triceratium Smithianum, n. sp., Grev. — Valve with slightly 
convex sides and rounded angles containing prominent pseudo- 
nodules; surface filled with closely radiating lines of very 
minute puncta, having a central space in which they are 
sparingly scattered ; margin very strong. Distance between 
the angles '0040^^ (Fig. 7.) 
Hab, Barbadoes deposit, Cambridge estate ; George J. 
Smith, Esq. ; E. K. G. 
This species was kindly communicated to me by its dis- 
coverer, Mr. G. J. Smith, of Workington, and the specimen 
accidentally destroyed, but not before I had made the 
drawing now engraved. Two other examples have subse- 
quently occurred to myself, which in all respects confirm the 
characters exhibited in the original specimen. This species 
is remarkable for the fine and extremely close radiating 
punctation which does not commence from the centre itself, 
but from the edge of a rather large half- blank space, in which 
a few puncta are remotely scattered. The strong margin is 
not striated. The pseudo-nodules are not large, but sharply 
defined, and are evidently very prominent. This diatom is 
allied to my T. connexum, but the structure is more minute, 
and the small, defined umbilicus of that species differs 
widely from the central half-blank space in T. Smithianium. 
Triceratium irregulare, n. sp., Grev. — Large; valve pale, 
with nearly straight sides and rounded angles, generally more 
or less unsymmetrical ; margin very slender ; cellules con- 
spicuous, radiating, and somewhat plumose, nearly equal in 
size ; angles within slightly concave. Distance between the 
angles -0040" to -0055". (Fig. 5.) 
Hab. Barbadoes deposit, Cambridge estate ; common. 
The most frequent of all the Triceratia which occur in the 
