Greville, on New Diatoms. 
83 
One of the most beautiful diatoms known^ and closely- 
allied to the preceding. In this case the radiating lines of 
the centre are genuine costse^ each of which, as it terminates 
at the margin of the inner triangle, becomes capitate, pro- 
ducing an exquisitely ornamental effect. The pseudo- nodules 
are large, flat, and oblong ; and an approach is made to the 
double pseudo-nodule of the preceding species, by their 
being traversed by two fine oblique lines, which, meet at the 
apices of the angles of the inner triangle ; and what brings 
the approach still closer, is the fact that it is the division 
next the angle of the valve only which is punctate. A re- 
markable peculiarity consists in the pseudo-nodules not being 
situated in the extreme angle, as in the other species of the 
group, but leaving space for the lateral costse to be visibly 
continued round them. These costse are widely separated 
throughout the greater length of the border, but increase 
rapidly in number as they turn round the angle, so that 
there are about twenty on each side. The angles of the 
inner triangle are lengthened out until they enter the punc- 
tate portion of the pseudo-nodule, and terminate in a short 
spine. In this and the preceding species the puncta in the 
lateral compartments are rather widely scattered. 
Triceratium Ahercrombieanum, n. sp., Grev. — Valve with 
nearly 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 fork with 
incurved apices, a faint, undulating line passing along the 
middle of each border. Distance between the angles, about 
•0023". (Figs. 7—9.) 
Hab. Barbadoes deposit, C. Johnson, Esq., Dr. Greville; 
extremely rare. 
At a hasty glance this might readily pass for a variety of 
the preceding species ; but the presence of a striated margin, 
and the totally different centre, immediately dispel the 
impression. The pseudo-nodule, besides, is single ; and 
although in one instance (fig. 9) the fork of the apex of the 
short line terminating the angles of the central triangle forms 
an enclosed, roundish space, instead of remaining open, it is 
unconnected with the pseudo-nodule, and contains puncta. 
A remarkable character in this species is a faint undulating 
line which passes along the middle of the border, commencing 
at the outer angle of the fork above mentioned, and ending 
at the corresponding point in the opposite angle of the valve. 
This line, which, although faint, may be traced without any 
difficulty, I have found uniformly present in the four specimens 
