64 
Grevillb,, on New Diatoms. 
radiating lines are continued from the margin to the apex, 
and divide the disc into faint but perceptible compartments. 
The surface is either plain or armed with variously arranged, 
minute spines. The first and last of the following species oc- 
curred to myself some years ago, when I was engaged upon the 
examination of Barbadoes earth, in working out the remarks 
able Asterolamprce contained in that deposit ; but no others 
had been observed, until my friend, Mr. Johnson, commenced 
the investigation of the sample of the deposit from Cambridge 
estate, which has yielded so prolific a harvest of beautiful 
and curious new diatoms. The species of the present genus 
not described in this paper will be published by Mr. Ralfs, 
along with many other new and remarkable objects, in the 
forthcoming supplement to Pritchard^s valuable work on the 
' Infusoria.^ 
Porodiscus elegans, n. sp., Grev. — Disc very convex, un- 
armed, divided into compartments by pairs of the radiating 
lines of very minute puncta, extending from the margin to 
the centre. Diameter -0020" to -0033". (PI. IV, fig. 1.) 
Barbadoes deposit, from Cambridge and other localities; 
C. Johnson, Esq., B.K.G. 
This species is distinguished by the disc being divided into 
numerous compartments, by pairs of radiating lines of puncta, 
very distinctly seen under a moderately magnifying power, 
and at the same time being quite destitute of spines. It is 
the most frequent species, three or four valves sometimes 
occurring in a single slide. The connecting zone is rarely 
seen in situ. 
Porodiscus major, n. sp., Grev. — Disc with a very large 
pseudo-opening ; the radiating puncta very minute, irregular, 
and interrupted for some distance round the opening, after- 
wards becoming regular, with faint, equidistant rays, formed 
by pairs of the longest lines. Diameter of pseudo-opening 
•0006". (Fig. 2.) 
Hab. Barbadoes deposit from Cambridge estate, in a slide 
communicated by C. Johnson, Esq. 
I have not seen an entire valve of this species, but from 
what remains in the specimen before me it is probably not 
less than '0040" or -0050" in diameter. The margin of the 
pseudo-opening is somewhat crenate or plicate, in consequence 
of the lines of puncta being somewhat thickened at their 
tarmination. From its large size, it is easily seen that there 
js no real perforation; and that it is simply concave, and 
closed by a diaphragm. For a space round the pseudo- 
opening equal to the diameter of the opening itself the 
puncta are exceedingly irregular; many of the radiating 
