84 
Greville, on New Diatoms, 
Triceratium. 
Triceratium zonatum, n. sp.^ Grev. — Small; valve with 
nearly straight sides^ and obtuse angles, furnished with round- 
ish pseudo-nodules ; surface minutely punctate, with a circular 
blank umbilicus, and with the angles cut off by two broad 
blank lines. (Fig. 3.) 
Hab. Barbadoes deposit, Cambridge estate; C. Johnson, 
Esq. 
A handsome and striking little diatom. Pseudo-nodule 
filling up the external angle. Surface closely and minutely 
punctate, with a row also of minute puncta (15 in -OOl"") 
along the margin. Umbilicus distinct, smooth, circular. 
Angles separated from the centre by two blank lines or 
bands ; the first situated considerably nearer the centre than 
the apex ; the second just beneath the angle itself, there being 
only a single row of puncta between them. Distance between 
the angles about '0030'^ The species to which this diatom is 
most nearly allied is T. cellulosum, Trans. Mic. Soc.,^ 
vol. I, N. S. Plate iv, fig. 14.) A.t the same time the 
dififerences are so marked that it is quite unnecessary to 
point them out. 
Triceratium pallidum, n. sp., Grev. — Small; valve with 
straight sides, subacute angles, 4 — 6 short vein-like lines 
given off from the margin, and the whole area filled with 
scattered puncta, larger in the centre, extremely minute to- 
wards the margin and in the angles. (Pig. 7.) 
Hab. Barbadoes deposit, Cambridge estate. 
I am not acquainted with any species to which the present 
one bears any affinity unless it be T. areolatum, which it 
somewhat resembles in outline and in the sharp vein-like 
marginal lines. In other respects the structure is totally 
dissimilar. The distance between the angles is '0030"'. 
Triceratium definitum, n. sp., Grev. — Small ; valve with the 
sides straight in the middle, the angles broadly ovate, with 
transverse lines of separation, which convert the interior into 
a nearly equal hexagon ; pseudo-nodules large ; surface filled 
with lines of minute radiating puncta, the margin with a row 
of larger puncta. (Fig. 8.) 
Hoi. Barbadoes deposit, Cambridge estate; C. Johnson, 
Esq. 
This species approaches T. insigne, but differs in various 
essential particulars. That somewhat variable diatom, of 
which I have examined a considerable series, has the sides 
