BALANUS TINTINNABULUM (_var._) _Chenu._ Illust. Conch., Tab. 2, fig.
8.
_Shell globulo-conical, often elongated in the rostro-carinal axis,
pale pink, smooth, extremely massive: parietal pores, close to the
basal margin, circular and very small. Scutum with the articular ridge
broad and reflexed._
_Hab._--Philippine Archipelago, attached to _Millepora complanata_,
Mus. Cuming. Mus. Brit. and Stutchbury.
_General Appearance._--Shell globulo-convex, sometimes much elongated
in its rostro-carinal axis; smooth; walls excessively strong,
massive, and heavy. Orifice oval, rather small in proportion to the
size of shell, this being chiefly due to the infolding of the upper
part of the rostral compartment. Parietes pale pink, feebly tinted
with purple: radii either paler, or tinted of a bright chesnut-brown:
sheath rich purplish chesnut-brown. Basal diameter of the largest
specimen nearly 3-1/2 of an inch; height 2-3/4: another specimen had
a basal longitudinal diameter of 2.9 of an inch, and a transverse
diameter of only 1.6; this great difference in the two diameters
being caused by the prolongation of the basal portion of the rostrum
in the line of the branch of the Millepora, to which the shell had
adhered; the height of this same specimen was 1.5; and the diameter
of the orifice, both transversely and longitudinally, .75 of an inch.
_Scuta_, broad, feebly tinted with pink; exterior surface rough,
with sharp hood-formed projections, arranged in straight lines
radiating from the apex; an inflected portion of the valve along the
tergal margin is not roughened. Internally (Pl. 3, fig. 1 _d_), the
articular ridge is broad and reflexed. An adductor ridge can hardly
be said to exist, but a slight prominence borders the gentle hollow
in which the lateral depressor muscle is attached. The basal margin,
on its inner face, is slightly toothed. _Tergum_ white, with the
narrow part of the valve, on the scutal side of the spur, rough with
the little projecting hoods, like those on the scutum; the other and
larger half is smooth: spur rather long, narrow, placed at twice its
own width from the basi-scutal angle; on the carinal side, about half
of the basal margin slopes down towards the spur. The longitudinal
furrow is either quite or nearly closed. Internally, the spur is
produced upwards on the valve, as a prominence: the articular ridge
is not very prominent. There are no crests for the tergal depressor
muscle.
Altogether the opercular valves strikingly resemble those of _B.
tintinnabulum_, but all the characters above mentioned have not been
observed in any one variety of this species; perhaps _var. coccopoma_
comes nearest, both in the external appearance of the shell and in
the structure of the opercular valves, to _B. Ajax_.
The _Compartments_ are remarkably compact and solid; the parietal
tubes are cylindrical and quite minute even close to the basis; they
extend, however, nearly up to the top of the shell; the parietal
septa at the basis are thick, and with blunt denticuli; the thickness
of the walls in the upper part of the shell is excessive; in the
lower part, it is also unusually great, owing to the thickness of the
inner lamina, and hence the ribs, generally formed by the projection
of the longitudinal septa on the inner lamina, are here visible only
close to the basis. The _radii_ are rather wide; their summits are
parallel to the basis; the septa on their sutural edges are thin,
straight, and closely approximate, and most symmetrically furnished
with little denticuli of equal sizes on both sides: the interspaces
are nearly filled up solidly, but with some pores still left open.
In the upper part of the shell, the radii, like the walls, are of
extraordinary thickness: the septa are transverse and horizontal,
as seen externally by slight variations in the colour of the radii;
internally, as seen in a vertical section of the shell, the septa
dip inwards at an angle of above 45°. The _alæ_ are thin, and have
their summits oblique: their sutural edges are smooth. The pores in
the basis are crossed by numerous transverse septa, and there is an
underlying cancellated layer: the internal surface is very smooth.
_Animal's body_ unknown.
The strength of this Balanus is truly remarkable; and when, by
repeated blows, a specimen which I was examining at last yielded,
the radii broke sooner than separate at their sutures. In most of
its characters, this species approaches _B. tintinnabulum_, and I
believe has been included by Chenu as one of its varieties; but
it comes almost equally near to _B. stultus_, to which it is much
more closely allied in its habit of being attached to Milleporæ.
By a close and unbroken chain of affinities, _B. Ajax_, through _B.
stultus_, is connected with _B. calceolus_ and its allies in section
(B), which live attached to Gorgoniæ. Some of the specimens of _B.
Ajax_, are almost as much elongated in their rostro-carinal axis, as
are the species in section (B); and there is an affinity in the same
direction in the smallness of the pores in the radii of _B. Ajax_;
indeed, had the basis in this species been generally more boat-or
cup-formed, I should have placed it as the first species in section
(B), instead of, as at present, the last species in section (A). The
intermediateness of the characters of _B. Ajax_ has been one chief
cause why I have rejected the genus Conopea, which was instituted by
Say for the species living attached to Gorgoniæ.
_Section_ B.
_Parietes and basis sometimes permeated by pores, sometimes not: radii
not permeated by pores: shell elongated in its rostro-carinal axis:
basis boat-shaped: attached to Gorgoniæ and Milleporæ._