TRANSACTIONS. 
Descriptions of New and Rare Diatoms. Series IX. 
By E. K. Greville, LL.D., F.R.S.E., &c. 
(Communicated by F. C. S. Roper, F.R.S.) 
(Read May 13tli, 1863.) 
(PI. IV and Y.) 
The species described in this paper were obtained from a 
sample of Barbadoes earth (Cambridge estate), communicated 
a few months ago to my veteran friend in diatomic research, 
Mr. Johnson, of Lancaster. Extensively as this remarkable 
deposit had been examined, it is most extraordinary that in 
the small sample referred to, a host of new things — genera 
as well as species, should have been discovered ; while it is 
equally curious that many forms common in previously 
examined portions of the same deposit should here be 
absent. Some of the most singular as well as beautiful of 
these diatoms are in the hand of my friend and acute fellow- 
labourer, Mr. Ralfs, and will enrich the supplement to 
Pritchard^s ' History of Infusoria/ upon which he is at present 
engaged. 
PoRODiscus, nov. gen., Grev. 
Frustules free, disciform, composed of two discs, united by 
an intermediate, ring-like zone ; discs very convex, minutely 
radiato- cellulate or punctate, with a conspicuous central 
pseudo-opening or pore. 
This genus is evidently closely allied to Co scino discus, 
differing chiefly in the remarkable pore-like pseudo-opening, 
which is not a mere blank circular space produced by the 
absence of cellulation at the apex, but a well-defined, concave, 
apparent orifice, provided with a thickened margin. All the 
species hitherto discovered — and they are confined to the 
Barbadoes deposit — are very convex, with a minute structure 
of distinctly radiating puncta (cellules under a suflficiently 
magnifying power) . In nearly all the species certain of the 
VOL. XI. / 
