GrevillE; on New Diatoms. 
93 
We have here another diatom with the outline closely re- 
sembling that of T. orbiculatvm and of my T. convewiim,'^ but 
differing conspicuously in the absence of pseudo-nodules, 
the character of the punctation, and in the peculiarly strong, 
coarsely striated border. The latter is the broadest in the 
middle of each side, and becomes gradually narrower towards 
the angles, which show no pseudo-nodules. The puncta are 
oblong and distant in the centre, and become rounder, smaller, 
and closer as they approach the margin. 
T'riceratium Roperianum, n. sp., Grev. — Small; valve with 
nearly straight sides, rounded angles, and no perceptibl.; 
pseudo-nodules; striae few, thick, moniliform, very short, 
marginal, 7 in '001". Distance between the angles '00 18". 
(Fig. 8.) 
Hab. Indian Ocean soundings in 2200 fathoms, made by 
Captain Pullen. 
One of the most distinct species of the whole genus, and 
allied to T. margaritaceum, Harris onianum, and giganteum. 
The short strise, which constitute a marginal band, are of equal 
thickness throughout, and although moniliform,, have a sort 
of semicostate appearance. By careful adjustment the centre 
is seen to be filled up with cellules, large for so small a species, 
and too delicate to be represented in the engraving. In this 
respect, as well as in the thick moniliform strise, its affinity is 
shown to the species above mentioned. 
I have much pleasure in dedicating this species to the dis- 
tinguished diatomist who kindly presented me with a portion 
of the Indian Ocean soundings, containing the Aster olamprce, 
already published in the Society^s Transactions, and the four 
species of Triceratium now described. 
Triceratium flescuosum, n. sp., Grev. — Small; valve thin, 
* A question has been started whetlier this species be T. orhiculatum. 
I have not seen a single valve the side view of which coines at all near to 
my T. convexum in slides from Mauritius or the East Indies ; but a slide 
from the Sandwich Islands, submitted to my ins{)ection by Professor 
Walker- Arnott, contains side views more nearly resembling it, and it is pos- 
sible that the two may be identical, viz., my T. convexim and T. orbiculatum 
of Brightwell. With regard to the T. orhiculatum of Shadbolt, I have had 
an opportunity of examining the original specimen, now in the possession of 
Mr. Tuffen West, and find, as I anticipated, that the figure engraved by liim 
in ' Mic. Trans.,' vol. ii, PI. I, fig. 6, is correct, with tlie exception of the 
omission of a row of marginal puncta or granules, 14 in "OOl The cellulation 
is, as there represented, roundish, nearly equal in size throughout, and not 
exhibiting the very slightest indication of radiation from the centre — an or- 
ganic difference so important in my view as to separate it at once from 
T. orhiculatum of Brightwell, although the front view of the valve should prove 
to be very similar. Indeed, there is no reason why the general character of 
the front view in that diatom should not be common to several species. 
