48 
Greville, on New Diatoms. 
posit of the Springfield estate, by Mr. Hardman ; from that 
of the Cambridge estate, by Mr. Johnson and myself. It 
appears, however, to be extremely rare. The diameter is 
upwards of '0050''; but, as in the other species, the size is 
probably exceedingly variable. A. ornaius is sometimes 
very small ; but I have a disc before me *0200'' in diameter, 
belonging to Mr. Hardman^s cabinet. 
Cestodiscus^ n. gen., Grev. 
Frustules disciform (circular or oval) ; disc with radiating 
granules or cellules, and a submarginal circle of obtuse pro- 
cesses unconnected by means of special radiating lines of 
cellules with the centre. 
The diatoms which I propose to comprehend under this 
name would be Aulacodisci if any communication existed 
between the processes and the centre of the disc. But no 
such communication does exist, and the question consequently 
arises whether they ought to be united with Eupodiscus, of 
which Aulacodiscus itself, according to Kiitzing, is only a 
section, or kept altogether apart. Taking Eupodiscus as it 
stands, it is anything but a natural genus, and the time is 
probably not far distant when the non-radiant species, at least, 
furnished with mastoid^ processes similar to those of Auliscus, 
will be grouped into a distinct genus. Looking, then, upon 
Eupodiscus Argus as the type of that genus, I cannot bring 
myself to do such violence to nature as to place the beautiful 
little discs now under consideration beside it. At the same 
time I honestly confess that the best generic character I can 
frame is weak, and I can do little more than rest for the 
present upon the natural feature unknown among the Eupo- 
disci of numerous equidistant intramarginal processes. 
CestodiscusJohnsonianus, n. sp.,Grev. — Disc small, circular, 
with subremote lines of radiating granules of various lengths, 
passing suddenly towards the margin into a band of minute 
puncta; processes very numerous. (Fig. 8.) 
Hab. Moron deposit, in the Province of Seville; C. John- 
son, Esq. ; R. K. G. 
A small, pale diatom, apparently extremely rare, as Mr. 
Johnson and myself have only found one specimen each. At 
first sight it would pass for an unquestionable Aulacodiscus ; 
but, as its excellent discoverer remarked, there are positively 
no channels of communication, nor special parallel lines of 
granules, between the processes and the centre. I have given 
these discs the most careful examination, and can certify the cor- 
rectness of my friend^s statement. The processes are arranged 
