92 
GiiEviLLE^ on New Diatoms. 
four corners and four processes^ and the greater part of the 
radiating costae concealed by a foreign body placed in the 
middle of the disc^ we should have much the appearance pre- 
sented by the diatom now under consideration. The centre 
of the nucleus is distinguished by a small, circular umbilicus_, 
from which emanate pale and slender rays^ such as artists 
conventionally represent as given oft' from a point of brilliant 
light. There is also a border to the nucleus, Avithin which it 
appears to be somewhat concave. The distance between the 
processes is about '0012", while that across the disc is about 
•0015". It is remarkable how rarely this strange little object 
is found in a perfect state. The most perfect example which 
I have seen^ and which I have represented_, is in Mr. George 
Norman^s cabinet. The surface appears to be generally more 
or less abraded ; and the radiating costse^ which form a some- 
what prominent ridge^ is the first part to be injured. In 
proportion to the extent and degree of abrasion, the surface 
presents different aspects ; the outline of the nucleus some- 
times almost entirely disappearing. The four processes, how- 
ever, are always conspicuous, shining like brilliant eyes, even 
under a moderate power of the microscope. 
TuiCERATIUM. 
Triceratium pectinatum, n. sp., Grev. — Valve with some- 
what rounded sides, and broadly rounded angles; surface 
filled up with small, distinct cellules, radiating from the centre, 
and increasing in size until near the margin, which is fur- 
nished with very strong pectinate striae^ 10 in '001". Dis- 
tance between the angles^ -0040". (Fig. 6.) 
Hab. India; obtained from shell-scrapings. Mr. George 
Norman^s cabinet. 
This fine species bears a general resemblance, in outline 
at least, to T. orbiculatum ; but difi*ers in the very broadly 
rounded angles, undeveloped pseudo-nodules^ much larger 
cellulation, and, above all, in the presence of exceedingly 
strong, sub- distant marginal strife. These striae are confined, 
and do not extend to the angles themselves. 
Triceratium decorum, n. sp., Grev. — Valve with convex 
sides and somewhat obtuse angles ; striae radiating from the 
centre, composed of pale puncta, becoming gradually smaller 
and closer towards the margin ; the latter rather broad, nar- 
rowing off at the angles, marked with coarse striae, 11 in -001". 
Distance between the angles -0028". (Fig. 7.) 
Hab. Indian Ocean soundings in 2200 fathoms, made by 
Captain Pullen. 
