74 
Greville_, on New Diatoms. 
This beautiful genus appears to be a very natural one ; its 
cliaracteristic feature being the coronal circle of large cellules, 
and the curved or spiral arrangement of the cellules within 
the circle. The typical species, B. coronata, has never, I 
believe, been found entire, the greater portion of the border 
being always absent. On two occasions only have I obtained 
a fragment in which, along with part of the corona, was a 
portion of perfect margin. Do the coronal cells in this species 
invariably retain their oblong character ? Examples have 
certainly come under my notice in which they were more round 
than oblong, but I unfortunately omitted to mark them. It 
is, however, by no means improbable that the valves referred 
to may belong to an undescribed species. 
Triceratium. 
Triceratium notabilis, n. sp., Grev. — Large. Valve punctate, 
with straight sides ; angles broad, much produced, dilated, 
oblong Or somewhat rhomboidal, with a conspicuous pseudo- 
nodule j centre convex, with radiating puncta and several 
spines. Distance between the angles -0025'' to -0040". 
(Figs. 2, 3.) 
Hub. Barbadoes deposit ; rare. 
Of this fine diatom above a dozen examples, including 
broken specimens, have come under my observation. It is 
evidently related to T. coniferum, but is a much larger species, 
and conspicuous for the very produced angles, which are equal 
in length to the straight sides of the valve. The prevailing 
form of the angle is rhomboidal, but it is occasionally oblong, 
as in fig. 3. The centre of the valve is convex, and the 
puncta radiating as in T. coniferum, a character omitted to be 
brought out in the figure of that species in the ' Microscopical 
Journal.^ The centre is also furnished with spines, no 
fewer than seven being present in fig. 3, while in the specimen 
represented at fig. 2, two are situated at the base of each 
angle. The Barbadoes deposit has yielded me several other 
frustules, which form ahighly characteristic little group, of which 
T. coniferum may be regarded as the type, but whether some 
of them ought to be considered species or mere varieties is 
extremely difficult to say. They all agree in the radiating 
punctation, convex centre, spines, and pseudo-nodules, but 
differ considerably in form and relative proportions. Of these 
diatoms figures will be given on a future occasion. 
Triceratium microcephalum, n. sp., Grev. — Valve with con- 
vex sides and slender, produced, subcapitate angles, furnished 
with pseudo-nodules ; entire surface, except a small, central. 
