_Shell reddish-brown: radii broad, with their upper margins not
oblique, or only moderately oblique; sutural edges with plainly
denticulated septa: basis porose. Scutum without an adductor ridge;
tergum with the spur rather narrow._
_Var._ (_a_) (Pl. 8, fig. 10 _b_, 10 _c_), _with the shell elongated
in its rostro-carinal axis; basis narrow, clasping the stem of a
zoophyte; lateral compartments much broader than the almost linear
rostrum, carina, and carino-lateral compartments_.
_Var._ (_b_), _with rough longitudinally folded walls, and with the
summits of the radii forming an angle of about 45° with the basis_.
_Fossil_ in Coralline Crag, Sutton and Gedgrave; attached to
foliaceous Bryozoa; Mus. S. Wood, Bowerbank. _Var. a_, Coralline
Crag, Sutton, attached to cylindrical branches of corals; Mus. S.
Wood. _Var. b_, attached to shells, Osnabruck, Hanover, Mus. Lyell;
Bünde, Westphalia, Mus. Krantz.
My materials consist of a beautiful series of specimens in Messrs.
Wood and Bowerbank's collections; but unfortunately only a single
young specimen had its opercular valves preserved. Not one specimen
of the very curious variety (_a_) had opercular valves, yet I
cannot feel any doubt about its being only a variety, caused by its
attachment to a thin cylindrical branch of a coral, instead of to a
foliaceous Bryozoon; it will, however, be convenient to give a separate
description of this very remarkable form. With respect to var. (_b_),
both sets of specimens came to me with the name _B. stellaris_, of
Bronn; but as Bronn distinctly states, that in his species the parietes
are porose, and as such is not here the case, this cannot possibly be
that species: these specimens did not possess their opercular valves,
and therefore cannot be identified with certainty.
_General Appearance._--Shell conical, with the orifice rather large,
and rhomboidal. The surface is very smooth, except in var. (_b._)
from the Continent, in which it is rugged and longitudinally folded.
The colour is ochreous-brown (chiefly no doubt derived from the
imbedding substance) tinged with red. The radii often have a much
darker and more distinct red tint; they are sometimes longitudinally
striped with dirty white. The radii are broad, with their summits
straight, and very slightly oblique; in _var. b_, however, they slope
at an angle of about 45°. Basal diameter of largest specimens .6 of
an inch; but this is an unusual size.
_Scuta_ (from a young individual), with the growth ridges little
prominent. Internally the articular ridge is moderately prominent,
with its lower end very obliquely rounded off; there is no adductor
ridge; there is a minute pit for the lateral depressor muscle.
_Terga_, with a slight longitudinal depression extending down to the
spur: spur short, with its lower end almost square or truncated,
about one fourth of width of valve, and placed at about half its own
width from the basi-scutal angle. Internally, the articular ridge is
prominent; the crests for the tergal depressores are feebly developed.
_Parietes_, moderately thick and generally strongly ribbed
internally, without parietal pores. _Radii_, wide, with their upper
margins straight, not smooth or rounded, and very slightly (or, in
_var. b_ moderately) oblique; their sutural edges have well-developed
septa, which are denticulated: the interspaces between the septa
are filled up solidly. The _alæ_ have their upper margins oblique:
they are only slightly, and sometimes not at all, added to above the
level of the opercular membrane: their sutural edges are smooth. The
_basis_ is thin, but plainly porose.
_Var._ (_a_).--With respect to this remarkable variety, any one
would at first think it specifically distinct. The shell is much
compressed, or elongated in the rostro-carinal axis, sometimes to
a great degree; I have seen a specimen .25 of an inch in this axis
and only .1 in its broadest part; but this is a very unusual degree
of elongation. The most remarkable character is the extraordinary
narrowness of the carina, the carino-lateral compartments, and of the
rostrum, compared with the great breadth, especially along the basal
margin (Pl. 8, fig. 10 _b_, 10 _c_), of the lateral compartments.
The radii are of unusual breadth. The tips of the rostrum and of the
lateral compartments are a little arched in, tending to make the
shell somewhat globular. The true basis is extremely narrow (fig.
10 _c_): it is deeply grooved, from clasping the thin, cylindrical
stem of the coral to which it had adhered; and I have seen specimens
in which the opposite edges of the groove had met, a tube having
been thus actually formed. From the grooved basis, and from the
elongation of the shell in the rostro-carinal axis, this species
presents so close a general resemblance to _Balanus calceolus_, and
its allies, that I have seen it in a collection arranged on the same
tablet with a fossil specimen of _B. calceolus_. Notwithstanding
the above several strongly-marked characters, by which this variety
differs from the ordinary form, there is a resemblance in colour and
aspect, which though difficult to be described, made me from the
first suspect that the two were specifically identical. In no point
of real structure is there any difference, excepting that, perhaps,
the pores in the basis are here rather smaller; but this might arise
from the little development of the peculiar basis. Having come to
this conclusion, I was interested by finding a specimen in Mr. Wood's
collection, which had originally fixed itself (judging from the form
of the basis) on a cylindrical stem, but which had subsequently grown
on to an adjoining flat surface; consequently, one side of the shell
presented all the peculiar characters of the present variety, whereas
the other side, at the rostral end, was undistinguishable from the
ordinary form. The unequal development of the rostrum on the two
sides was very striking, and clearly showed how great an effect could
be produced by the nature of the surface of attachment.
This singular variety cannot be considered accidental, in the sense
in which this term may be applied to some varieties: the larva
evidently fixes itself intentionally, in a certain definite position,
on the branch of the coral (when a branch is chosen), exactly as in
the case of _Balanus calceolus_, or _Scalpellum vulgare_. But when
other species of Balani occasionally fix themselves on branched
corals, their position seems to be accidental and unsymmetrical; thus
among the symmetrically elongated specimens of the present species, I
found one specimen of _Balanus bisulcatus_, which had evidently been
attached in an almost transverse position to a branch, and had thus
become much distorted; so, again, I have seen specimens of the recent
_B. amaryllis_ attached irregularly to a Gorgonia, in the midst of
the symmetrically elongated shells of _Balanus navicula_, an ally of
_B. calceolus_.
This variety does not seem to attain so large a size as the ordinary
form.
_Affinities._--This species is allied to the two last described
fossils, namely, _B. varians_ and _unguiformis_, but is perhaps
more nearly related to the recent _B. allium_, an inhabitant of
the Barrier Reef of Australia. The longitudinally folded variety
(_b_) can hardly be distinguished by external aspect, or even
by the opercular valves, from _B. crenatus_; but when the shell
is disarticulated, the porose walls and non-porose basis of _B.
crenatus_, allow of no mistake in the diagnosis of the two species.