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NEW FORMS OF MARINE DIATOMACEZ. 537 
into two equal valves. The frustules are united by means of a circle of numer- 
ous short, terminal processes of equal length, which ultimately separate in the 
middle; and the detached frustules then appear furnished at each end with a 
beautiful coronet, or circle of miniature turrets. This mode of connection is peculiar, 
although perhaps analogous to that in Biddulphia. In the subject of these 
remarks, however, the connecting processes do not appear to be so distinctly a 
continuation of the substance and structure of the body of the frustule, as are the 
horns of that genus, and must rather be regarded in the light of appendages. 
With regard to the affinities of this beautiful little object, we may certainly 
assume, that if a solitary frustule had alone been formed it would have been 
referred by Kirzinc at once to the genus Pyzidicula. But little or nothing is 
known of the real nature of the variety of forms brought together under that 
name. EXRENBERG’s own character for the original genus is as follows :— 
* Animal e familia Bacillariorum, liberum, lorica simplici, bivalvi (silicea) ; 
solitarium, globosum (=Gallionella divisione spontanea perfecta aut nulla). Die 
Infusionsthierchen, p. 165. 
But EuRENBERG subsequently constituted other genera or subgenera to receive 
the accumulating species; and as the work in which they appear is not generally 
accessible, I do not hesitate to give the characters verbatim in this place. 
« Dictyopyxis, nov. gen. Pya«idicule generis ea bivalyes subglobos:e aut tur- 
gid formee, quze valvularum teste strictura simpliciter cellulosa insignis sunt ab 
lis, quze continua et simplici membrana silicea includuntur, aut appendicibus 
variis instructz sunt, gravius differunt et facillime distinguuntur. Cellulosas 
igitur in Dictyopyxidis subgenere colligendas senserim. P. cruciata, Cylindrus, 
hellenica et Lens huic subgeneri nunc inscribende sunt.”—Lhrenb. Bericht. der 
Berl. Akad., 1844. P. 262. 
“ Stephanopyzis, nov. subgenus. Pyaxidicule generis bivalves turgid aut 
subglobosze formee, quze valvularum testz structura cellulosa insignes sunt et 
denticulorum, aculeorum aut membranz coronam in media quavis valvula gerunt 
in hoc Pyxidicule subgenere colliguntur.”—Lhrenb., 1. c., 1844. P. 264. 
« Xanthopyais, nov. subgen. Pywidicule subgenus bivalve turgidum sub- 
globosum. Valvularum teste silicee continue integerrimz nec cellulose, super- 
ficie hispida, setosa aut alata.”—LHhrenb., l.c., 1844. P. 264. ; 
Kirzine, in his Species Algarwm (1849), reunites the whole, giving twenty- 
two species, all of which, except two, are fossil. The frustules, according to him, 
are “non concatenata.” Mr CresweLu’s Diatom is, therefore, by a most import- 
ant character, excluded. Taking a simple frustule, and leaving the processes out 
of view, it much resembles Dictyopywis hellenica (Ehrenb. Microgeologie, tab. xx., 
fig. 32), and also Stephanopyxis appendiculata of the same work, tab. xviii., fig. 4 ; 
but that species has only a single tooth at each end, and is provided with a sort 
of narrow zone or annulus. _ It resembles still more closely Stephanopyxis apicu- 
VOL. XXI. PART IV. 7E 
