Mr. Ralfs.
A . II. i l .
Pond near Wormley, West End, Herts :
The greatest peculiarity of this species is, that frequently
the frustules cohere together in considerable numbers, so as
to form filaments apparently similar to those of Fragilaria,
but in all probability really distinct. If, however, the specimens
be dried or kept in water, these filaments will generally
be found broken up In the manner of a Diatoma.
The only species with which It needs to be contrasted is
Diatoma vulgaris, from which it may be distinguished by the
absence, or at all events the exceeding fineness of the striæ,
on the end surfaces of the frustule, as well as by the filaments,
which it usually forms.
The colour is stated to be green, not altering much in drying.
In my specimens it has been dark bi'own, changing to
a greenish hue in the herbarium.
The removal of this species from Fragilaria to Diatoma
will render that genus a natural and not an anomalous one.
71. B A C IL L A R IA Gmelin.
Char. Frustules sliding one upon the other.
Derivation. From hacillum, a small stick.
In the genus Bacillaria Ehrenherg includes not merely
the species of the two preceding genera, but likewise the singular
production which forms the type of the limited genus
Bacillaria.
1. Ba c il la r ia paradoxa Gmelin.
Plate X C I I I . Fig. 10.
Char. Frustules very many times broader than long, cohering
together in considerable numbers upon the same plane,
motive upon each other. In end view striated.
F. sonderbares Stahgenthier Miiller, Muller’s Kleine
Schriften v. Coze, p. 1. fab. 1. 8., 1782; Pinddyr Nye
Sämling af Dansk Vidensk. Sallsk. Skrift. 11. p. 277.
Vibrio paxillifer Müller, Animale. Infus. p. 54. t. 7.
f. 3. 7., 1786. Bacillaria paradoxa Cmelin, Linnæi
Syst. Nat. ed. xiii. vol. vi. 1788. Vibrio paxillifer L a mark,
Système des Anim, sans Vert. 1815. Bacillaria
palea Nitzsch, In part, Beiträge zur Infusorienkunde,
1817 ; Encyclopädie v. Ersch u. Gruber, 1821. Bacillaria
paradoxa Bory de Saint Vincent, Diet. Classique,
1822. B . Mulleri Bory, Encyc. Méth. 1824. Oscil-
laria paxillifera Schrank, Nov. Act. Nat. Cur. xi. 2.
p. 534. 539. Bacillaria Miilleri Turpin, Diet, des Sc.
Natur. Végétaux Acotyledones, 1828. Bacillaria paradoxa,
Abhandl. der Akademie d. Wissensch. zu Berlin,
1831, p. 83. ; 1833, p. 319. ; Ehr. Infus. p. 196. t. xv,
f. 1.
This is the most singular of all the Diatomaceoe, and the
most protean in the forms which it assumes ; the variety of
which results from the power which the frustules undoubtedly
possess of gliding one upon the other. Sometimes
the margins of the frustules correspond in position with
each other, and then an elongated lamina is formed similar
to th a t of the Fragilarioe. A t others the frustules are drawn
out from each other by two and three together, and the
margins are rendered uneven ; and again at others, each frustule
composing a frond is drawn out, so tha t it adheres but
by a very small portion of its length to the frustule or frustules,
one on each side, with which it is connected. Now
this disposition of the frustules could only be effected by the
possession of a power of motion the one upon the other.
Ehrenherg in his definition of this species makes use of
the following phrase, “ haccillis singulis alacriter mobilibus ; ”
and, again, in the definition given in French, “ les baguettes
vivement mobiles.” Now it ought not, I apprehend, to be
imagined, as the words quoted would lead us to suppose, tha t
the frustules possess each and individually a power of locomotion
centered in themselves, but merely th a t they are so