164 GREVILLE, ON DIATOMACESE. 
or sometimes bilobed, punctate, unarmed ; angular processes 
very short and obtuse, largely inflated at the base; con- 
necting membrane with rows of minute dots parallel with 
the suture of the valve. (Figs. 11—13.) 
Monterey, California ; Gear ge Norman, Esq. In Cali. 
fornian guano. 
This species appears to be removed from all the varieties of 
B. aurita by the absence of spines, and by the very depressed, 
often two-lobed central elevation of the valve. It differs also 
in the more distinctly punctate structure; in the more con- 
spicuous rows of dots in the connecting membrane, and in 
the angular processes being much shorter and more obtuse or 
rounded ; they are, indeed, sometimes so short, as to scarcely 
rise above the level of the central elevation, in which case 
the process and its inflated base appear almost like two 
lobes of the same organ (see fig. 12). The species has, 
like some of its congeners, a large range with regard to 
size, and the punctate structure is fine or coarse in proportion 
to the development of the frustule. Fragments of indivi- 
duals have occurred to me considerably larger than those I 
have represented. At all times it appears to be a much 
larger form than B. aurita. 
Since these observations were written, Mr. George Norman 
has kindly sent me a shde of Diatomacee, from Monterey, 
which he believes to have been collected from sea-weed. It 
contains, besides Biddulphia turgida and other things, several 
frustules of B. Roperiana, agreeing minutely with those I had 
found in the guano. 
I have much pleasure in dedicating to the acute and judi- 
clous expositor of the genus Biddulphia this very beautiful 
new species. 
CRrESSWELLIA, Arn. and Grev. 
In the ‘ Transactions of the Royal Society of Edinburgh,’ 
vol. xxi, I have assigned the reasons which led my friend 
Professor Walker-Arnott and myself to propose a new genus 
for the reception of the Diatom we there described and figured 
under the name of Cresswellia turris. I may here briefly 
state that Ehrenberg, having found that his original definition 
of the genus Py«idicula (‘ Die Infusionsthierchen,’ p. 165) 
required revision, constituted three sub-genera, Diciyopyzis, 
Stephanopywis, and Xanthopyxis (‘ Bericht. der Berl. Akad.,’ 
1844, p. 262, et seq.) It must be admitted, however, that 
so very litthé was known of the forms thus associated, that 
these sub-genera resembled artificial sections, adopted for 
mere convenience, rather than well-defined genera; and 
