84* 
Greville_, on New Diatoms. 
which I have had an opportunity of examining. By a reference 
to the plate it will be perceived that some variation is liable 
to occur in the lines at the angles^ as well as in the number 
of the lateral costse. The puncta are considerably more 
numerous than in T. marginatum. I have much pleasure 
in dedicating this diatom to my acute correspondent^ Dr. 
Abercrombie, of Cheltenham. 
Triceratium inopinatum, n. sp., Grev. — Yalve with nearly 
straight sides^ rounded angles^ and striated margin ; centre a 
blank triangular space ; border divided by transverse costse 
into minutely punctated compartments; a short line from 
each angle of the central triangle terminating in a small, 
roundish compartment, joined to the pseudo-nodule; no 
undulating line along the border. Distance between the 
angles -0020". (Fig. 10.) 
Hab. Barbadoes deposit ; extremely rare. 
The only question which can arise relative to the validity 
of the present species is whether it be not a variety of the 
preceding. Had the separation been proposed on account of 
the apparently double pseudo-nodule alone, I should have felt 
some hesitation. It might have been said that in one of the 
varieties of T. Abercrombieanum the short lines proceeding 
from the angles of the central triangle terminate in enclosed 
spaces, owing to the incurved apices of the fork becoming 
united ; and that if these enclosed spaces had been pushed 
forward to a junction with the pseudo-nodule, we should just 
have the appearance exhibited by the diatom now under 
consideration. It may be remarked, however, that the 
enclosed spaces above mentioned preserve their relative dis- 
tance from the pseudo-nodule, as distinctly as if the apices of 
the fork had remained open. In the present species there 
is, at first sight, the appearance of an actual double pseudo- 
nodule ; but it is an appearance only, the second one being 
merely the fork of the short line meeting at the base of the 
pseudo-nodule, and thereby indicating a different relative 
position of the parts from what occurs in the preceding 
species. In addition to what has been said, the total absence 
of the undulating line so remarkable in the border of that 
diatom seems to confirm the view I have taken of the pro- 
priety of regarding T. inopinatum as distinct. 
Triceratium approximatum, n. sp., Grev. — Yalve with 
straight sides, obtuse angles, and striated margin; centre a 
blank, triangular space ; border divided by transverse costae 
into punctated compartments ; a short line from each angle 
of the central triangle terminating in a wide, shallow fork ; 
pseudo-nodule single, sending out two spurs from the base ; 
