Greville, on New Diatoms, 
71 
most remarkable. About half a dozen examples have been 
observed. The interval between the margin and the central 
labyrinth of lines is blank, with the exception of a few short, 
vein-like lines given off from the central network, some of 
which nearly reach the margin. In this, as in many other in- 
stances, a figure will convey a better idea of the object than 
the most elaborate description. 
Triceratium areolatum, n. sp., Grev. — Valve with slightly 
concave sides and acute angles ; surface covered with rather 
large, circular areolae, while very short, vein-like lines project 
from the sides of the valve. Distance between the angles 
•0026". (Fig. 13.) 
Hah. Barbadoes deposit ; extremely rare. 
I do not know any member of the genus with which this 
diatom can be compared, unless it be T. acutum, Ehr., with 
which it agrees in the rather peculiar areolation. From that 
species, however, it differs in the sides of the valve being 
decidedly, although slightly, concave, and in the angles not 
being in the smallest degree elongated. The short, vein-like 
lines present, in addition, a conspicuous differential cha- 
racter. Nevertheless, I am not certain of its being distinct. 
Triceratium tessellatum, n. sp., Grev. — Valve with straight 
sides and rounded angles, somewhat convex in the centre ; 
surface filled with subquadrate, large, more or less concentric 
granules, becoming smaller at the angles ; margin with a row 
of minute granules, 11 in *001". Distance between the angles 
•0025". (Fig. 14.) 
Hab. Deposit on the banks of Pertuxent River, near Not- 
tingham, Maryland, United States. 
Distinguished by the large size and more or less square 
form of the granules, especially those of the convex centre. 
Smaller granules completely fill up the angles. In some ex- 
amples the convexity of the centre is scarcely at all apparent. 
Triceratium robustum, n. sp., Grev. — Valve with straight 
or very slightly concave sides and rounded angles with 
pseudo -nodules ; surface filled with irregularly shaped, coarse 
granules, those in the circumference of the convex centre and 
at the angles small, the rest large. Distance between the 
angles -0030" to -0040 (Fig. 15.) 
Hab. Cove, Calvert County, Maryland, United States. 
A strong, coarse-looking species, with a large, clear, pseudo- 
nodular space at the angles. The granules are very irregular, 
small ones being often mixed with the large ones. Some- 
times a concentric arrangement is conspicuous, but in other 
cases it is very partial, being most distinct between the con- 
vex centre and the angles, where also the largest granules 
