BALANUS SPONGICOLA. _Brown's_ Illustrations of the Conchology of
Great Britain (1827), pl. 7, fig. 6: 2d edit. (1844), pl. 53,
figs. 14-16.
_Parietes generally smooth, sometimes longitudinally folded; coloured
pink: orifice toothed. Scutum longitudinally striated. Tergum, with the
apex produced, without a longitudinal furrow; spur truncated, about one
third of width of valve._
_Var. with the walls slightly folded longitudinally._
_Hab._--South coast of England, and Tenby in South Wales, often
imbedded in sponges; attached also to shells and rocks in deep
water; Mus. Brit., Jeffreys. Algiers, on Mytili and Serpulæ, with
_B. perforatus_, Mus. Mac Andrew. Madeira, with _B. tulipiformis_,
Mus. Lowe. Lagulhas Bank, Cape of Good Hope, on detached kelp, with
_B. Capensis_, Mus. Sir J. Ross. Imbedded in sponge with _Acasta
spongites_, Mus. Bowerbank. _Var._ West Indies.
_Fossil_ in Coralline Crag, Mus. S. Wood.
_General Description._--Shell tubulo-conical; orifice of moderate
size, rather deeply toothed; colour dull pink, or purplish, or dark
flesh-colour; sometimes the radii are paler, sometimes of the same
colour with the parietes. Surface smooth when well preserved, having
transverse rows of minute spines. In the West Indian variety the
walls are slightly or much folded, but I will describe this form
separately. Size of largest specimen (Mus. Jeffreys), .6 of an inch
in basal diameter.
_Scutum_, with fine ridges radiating from the apex, and with the
lines of growth, crenated: internally, the articular ridge is small,
adductor ridge short and barely distinct: there is a rather deep
and narrow pit for the lateral depressor muscle. The whole valve
is much thinner than in _B. trigonus_, which in most respects it
closely resembles. _Tergum_, with the apex pinkish purple, produced
or beaked, but the beak is not needle-like, as in _B. psittacus_
and its allies, for the carinal margin is perfectly preserved up to
the tip. Externally the valve is nearly flat, for the longitudinal
furrow is very shallow. The spur is about one third of the width of
the valve; its lower end is abruptly truncated: in European specimens
(1 _b_) the whole basal margin, on the carinal side, slopes down to
the spur in a straight line, which, together with the sharpness and
production of the basi-scutal angle of the spur itself, gives to the
whole valve a peculiar appearance: in the specimen (1 _c_) from the
Lagulhas Bank, the basal margin on the carinal side is a little more
hollowed out, but it is quite impossible to doubt about the specific
identity of these specimens: in the West Indian variety (1 _d_) the
basal margin on the carinal side forms a distinct but obtuse angle
with the spur. In all cases the crests for the depressor muscles are
very feebly developed.
The _Compartments_ have their radii developed to a rather varying
degree, with their summits oblique; hence the orifice is toothed:
the sutural edges of the radii have their septa barely denticulated;
the sutural edges of the alæ are smooth. The basis, as with the
other species of this section, is permeated by pores; yet I found
one specimen, from the Cape of Good Hope, with the basis apparently
solid, thus offering a very singular anomaly. In the specimen
imbedded in sponge, the basis, as viewed externally, is concave;
whereas in Acasta, which always inhabits sponges, the basis is highly
convex or hemispherical.
The _Mouth_ and _Cirri_ resemble those of _B. trigonus_, and I can
point out no distinguishing character.
With respect to the variety from the West Indies, I have seen two
sets of specimens differing somewhat in external appearance, one set
attached to a coral from St. Vincent's, and another set to an Avicula
from an unknown locality; at first I described these specimens, with
some hesitation, as a distinct species, and I am very far from sure
whether this would not have been the more correct course, although
I am unable to point out any sufficient diagnostic characters. This
form differs from the ordinary _B. spongicola_, in the walls being
more rugged, stronger, and slightly or deeply folded longitudinally;
in this latter case the shell in external aspect differs much from
ordinary specimens of _B. spongicola_; but this is a variation so
common that I dare not place any reliance on it. The colour is more
purple; the summits of the radii perhaps rather less oblique. In the
scuta the only difference is that the articular ridge seems rather
longer, and the adductor ridge perhaps more prominent: in the terga,
as already remarked, the basal margin on the carinal side does not
slope so straight into the spur. These differences I consider all too
slight to be of specific value. The difficulty in determining the
nature of this variety is added to by its approach to _B. trigonus_
in all those points in which it departs from the ordinary _B.
spongicola_, so that for a short time I was even tempted to consider
both these species as varieties of one form. But until _B. trigonus_
is found with its scutum longitudinally striated, and with its tergum
beaked, it can hardly be confounded with _B. spongicola_; for it
should be observed that when in _B. trigonus_ the rows of little pits
disappear from the scuta, as sometimes happens, though rarely, yet
these valves do not become longitudinally striated.
_Balanus spongicola_ occurs, mingled with _B. tulipiformis_, in the
Mediterranean, and by the external characters of the shell alone
cannot be distinguished from that species; but the striated scuta and
beaked terga suffice to separate them. Again, this species, at the
Cape of Good Hope, occurs mingled with _B. Capensis_, and from the
non-striped young varieties of that species, it can, externally, be
distinguished only by the beak of the tergum not being sharp like a
needle. I have seen a single, perfectly characterised specimen, with
its opercular valves preserved, found by Mr. S. Wood in the Coralline
Crag at Sutton, mingled with _B. inclusus_.