154 BRIGHTWELL, ON 
I have already (vol. v, p. 191) explamed the origin 
of the pseudo-nodule in Triceratium undulatum, and shown 
that it is only the stump of a long cylindrical horn 
proceeding from the centre of the triangular end of the 
frustule, and further investigation has resulted in the dis- 
covery that this and another species, about to be described, 
and which we propose to name Triceratium malleus, are m 
their living and perfect state, filamentous. 
Triceratium undulatum has also presented itself under an 
aspect different, I believe, from any hitherto observed among 
the Diatomacee, and the character of which cannot at 
present be satisfactorily determined. In this state the frustules 
are placed one at each end of a mucous envelope, and are 
separated from each other by the exact length of the horn 
before described, and which proceeds from the inner end of 
each frustule. The frustules themselves are surrounded by 
siliceous bands united together lengthwise, having at each end 
a thick fringe or comb of short bristles or setze. A horn also 
proceeds from the external end of each frustule of equal 
length with that from the internal, the whole presenting a 
very abnormal and puzzling appearance. Further investiga- 
tion may, and I think probably will, show that it is one of 
what P. Smith terms “ the phenomena attending the forma- 
tion of the reproductive body” in this genus, and which are 
at present so imperfectly understood. In the state above 
described, the frustules not unfrequently present on an end 
view, a four-sided form, either square, or with the sides 
deeply indented, confirming what we have before stated as to 
varieties of this kind in several other species. 
In the filamentous state these appearances are consider- 
ably modified, the bands of silex beg more absorbed into 
each other, the horns shorter, and the combs or fringes of 
bristles or sete not apparent. In this state the sutural 
division seems effected in the normal mode, resembling 
somewhat, in the individual frustules, that of Biddulphia 
Bailey. The end view of the frustules generally presents 
the appearance of a triangular valve of silex imbedded 
in a softer siliceous cushion, the sides of the valve having 
each three undulations or indentations, evidently produced 
by the bands before mentioned; but variations of this_ 
structure are not uncommon, and there is one variety in 
which all the sides of the valve are perfectly straight. 
The other filamentous species, called by us Triceratium 
malleus from its resemblance to Malleus vulgaris, is larger 
than Triceratium undulatum, is without horns, and has no 
bands of silex surrounding the valves as in that species. On 
