BALANUS PORCATUS. _Emanuel da Costa._ Hist. Nat. Test. Brit., p. 249
(1778).
LEPAS BALANUS. _Linn._ Syst. Naturæ (1767).
---- ---- _Born._ Testacea Mus. Cæs. Desc., Tab. 1, fig. 4, (1780).
---- ---- _Chemnitz._ Syst. Conch., 8 Band., Tab. 97, fig. 820,
(1785).
BALANUS ARCTICA PATELLIFORMIS. _Ellis._ Philosoph. Transact., vol.
50, Tab. 34, fig. 18 (1758).
---- SULCATUS. _Bruguière._ Encyclop. Method., Tab. 164, fig. 1
(1789).
LEPAS COSTATA and BALANUS. _Donovan._ British Shells, 1802-1804, Tab.
30, fig. 1, 2.
LEPAS SCOTICA. _W. Wood._ General Conchology, Pl. 6, fig. 3, sed non
_Lepas balanus_, Pl. 7, fig. 3, (1815).
BALANUS ANGULOSUS. _Lamarck_ (1818), in _Chenu_, Illust. Conch., Tab.
11, fig. 11.
---- TESSELATUS. _Sowerby_ (!). Mineral Conchology, Tab. 84 (1818).
---- SCOTICUS. _Brown._ Illust. Conch. Great Britain, Pl. 7, fig. 2,
sed non, Pl. 6, fig. 9 et 10 (1827); 2d edit., Pl. 53, fig.
1-3, 22, 23 et Pl. 54, fig. 1-3.
---- GENICULATUS. _Conrad._ Journal Acad. Philadelphia, vol. 6, part
2, p. 265 (1830), Tab. 11, fig. 16.
---- ---- _Aug. Gould_ (!). Report on the Invertebrata of
Massachussetts, fig. 9 (1841).
_Shell white, generally sharply ribbed longitudinally: radii with their
summits almost parallel to the basis. Scutum longitudinally striated:
tergum with the apex produced and purple._
_Var._ (_a_): _Walls without longitudinal ribs_. Mus. Brit., Cuming,
Stutchbury, Jeffreys.
_Hab._--South shores of England, Ireland, Scotland, Shetland Islands,
Iceland, Davis's Straits, 66° 30′ N.; Lancaster Sound, 74° 48′ N.
(Mr. Sutherland). Maine and Massachussetts, United States. China (?).
In deep water, common on shells, crustacea, and rocks, sometimes
imbedded in sponges.
_Fossil_ in the glacial deposits of Scotland, Uddevalla, and Canada;
in the mammaliferous and Red Crag of England; Mus. Lyell, Sowerby, S.
Wood, &c.
_General Appearance._--Shell conical, somewhat convex; white,
sometimes tinted yellowish, from the thin investing membrane;
the produced tips of the terga are purple: the parietes of each
compartment have from two to four strong, prominent, sharp, straight
longitudinal ribs; these are sometimes irregular, and rarely, as will
presently be described, they are absent. The radii are smooth and of
considerable breadth; their summits are nearly parallel to the basis
or only slightly oblique: hence the orifice is entire; it is rather
small and ovate, being broad at the rostral end, and very sharp and
narrow at the carinal end.
_Dimensions._--The largest specimens which I have seen from Great
Britain or Ireland, have been 1.3 of an inch in basal diameter:
in Mr. Cuming's collection, however, there was one much depressed
specimen from the Shetland Islands, 2.1 in basal diameter: a
regularly conical specimen from the coast of Massachussetts attained
a nearly equal diameter; out of the glacial deposits in the Isle of
Bute, Scotland, several specimens had this same diameter, namely, two
inches, and were even more steeply conical, being 1.85 in height;
some glacial specimens from Uddevalla and Canada, in Sir C. Lyell's
collection, were 1.7 in basal diameter. Hence, it appears, as we
shall presently see is likewise the case with _B. crenatus_ and
_Hameri_, that northern specimens, and those from the United States
and from the glacial deposits, often exceed in dimensions those from
Great Britain or Ireland.
_Scutum_: the lines or ridges of growth are broad and prominent;
they are divided into square beads by fine striæ, radiating from the
apex: and hence the valve is longitudinally striated. Internally,
the articular ridge is extremely little prominent; the adductor
ridge, or what must be called such, runs straight down under the
articular ridge, making a deep longitudinal pit for the lateral
depressor muscle. _Tergum_: the apex is a little produced, and
coloured purple, as well as the upper internal surface of the valve;
there is no longitudinal furrow, only a very slight depression: the
spur is placed close to the basi-scutal angle; it is rather long,
and measured across the upper part, is half as wide as the valve:
its lower end is truncated and rounded; the basal margin slopes
towards it. Internally, a very small portion of the scutal margin is
inflected: the articular furrow is shallow and broad: the crests for
the depressores are feeble. In young specimens the spur is bluntly
pointed.
The _Parietes_ (4 _e_) have large square parietal tubes: in the
upper part these are filled up solidly without transverse septa:
the longitudinal septa are finely denticulated at their bases, and
the denticuli extend unusually close to the outer lamina. In very
young specimens the inner lamina of the parietes is ribbed, in lines
corresponding with the longitudinal septa, as is the case with most
species of the genus; but in medium and large-sized specimens,
there are between the ribs, thus produced, from one to four smaller
ribs, which do not correspond with any longitudinal septa; they are
finely denticulated at their bases, and may be considered as the
representatives of longitudinal septa which have not been developed
and reached the outer lamina. I have seen no other instance of this
structure, namely, the presence of a greater number of ribs, on
the inner lamina of the walls, than there are longitudinal septa.
The _radii_ have their summits generally parallel to the surface
of attachment, as is usual in the first section of the genus, but
sometimes they are slightly oblique: the septa sometimes rudely
branch a little, but they exhibit scarcely a trace of denticuli: the
interspaces are filled up quite solidly. The _alæ_ have their summits
very oblique; their sutural edges are finely crenated.
_Basis_, rather thin, translucent, not permeated by pores; obscurely
furrowed in lines radiating from the centre: the circumference is
marked in a peculiar manner by the longitudinal septa, and by the
tips of those intermediate, denticulated ribs, which occur on the
inner lamina of the parietes.
_Mouth_: labrum with six teeth: mandibles with the fourth and fifth
teeth small and rudimentary: maxillæ, with a small notch under
the upper pair of spines; in the lower part there is a single
large spine. _Cirri_, dark brownish purple, making a singular
contrast with the white operculum and shell; first pair, with one
ramus, having twenty-six segments, and about twice as long as the
shorter ramus, having twelve or thirteen segments, with their front
surfaces protuberant. In the second pair the segments are but little
protuberant: third pair about one third longer than the second pair:
sixth pair, elongated, having in the same individual forty-six
segments; these segments have shield-shaped fronts, bearing five
pairs of spines, with some minute intermediate bristles. There is the
usual point at the dorsal base of the penis.
_Range: Geological History._--This species is common on the shores
of Scotland and Ireland; the most southern point of Europe whence I
have happened to see a specimen is Tenby, in South Wales: but I have
no doubt it is found further south; and Mr. Jeffreys, who knows this
species well, has found it common on the extreme southern shores of
England. In the United States, it is found on the shores of Maine and
Massachussetts: northward, I have seen specimens from Iceland, from
Davis's Straits, and from Lancaster Sound, in lat. 74° 48′ north;
these latter I owe to Sir J. Richardson. It is an inhabitant of deep
water; in Mr. Thompson's collection there are several specimens from
the Bay of Belfast, marked twenty-five fathoms, and one group said
to have come from "about fifty fathoms, on the coast of Antrim:" one
specimen from Cape St. Anne, Massachussetts, is marked as having come
from only five fathoms. This species is commonly associated, on both
sides of the Atlantic, with _B. crenatus_, and sometimes with _B.
Hameri_ and _Verruca Strömia_: mollusca, such as pectens, modioli,
and oysters, offer the most usual surfaces of attachment: I have,
however, seen many specimens on crustaceans, on rocks, and even on
the roots of the larger sea-weeds. This species is very common in the
glacial deposits of Uddevalla, of Skien in Norway, and of Canada, and
is associated with the same species as in the living state: I have
seen, also, specimens from the same formation in the Island of Bute,
Scotland. I have seen numerous specimens from the mammaliferous crag,
and a few from the Red Crag of England. I owe to the kindness of Mr.
J. de C. Sowerby an inspection of the original specimens of the _B.
tesselatus_ of the Mineral Conchology, which is certainly the present
species.
_Affinities._--This species is very distinct from every other; it
comes nearest, as shown in all the characters derived from its
opercular valves, to _B. nubilus_, and in this latter species we
have seen the basis plainly tending to lose its pores and thus
become solid. _B. porcatus_ is perhaps allied in some degree to _B.
trigonus_, and slightly to _B. crenatus_. The rather broad radii,
with their summits hardly oblique, give this species a very different
aspect from those species of the genus amongst which it must be
placed.
_Varieties._--A conical specimen, sent to me from the coast of
Massachussetts, is remarkable from the radii not having been at all
developed, being represented by mere fissures. I have seen a few
specimens of _var._ (_a_), (one collected by Sir E. Parry in the
arctic seas) which had a remarkably different aspect from the common
forms, but which, after a careful examination of the opercular valves
and of the animal's body, I feel convinced are not specifically
distinct: they are characterised by the walls being smooth and
absolutely destitute of the external longitudinal ribs; by the shell
being more cylindrical, with broader radii, and with the orifice
larger and more rhomboidal; the walls and radii are much thinner, and
the internal lamina is less plainly ribbed: the beak of the tergum is
not purple. As most of these specimens had grown in a group crowded
together, the difference of shape, and perhaps the thinness of the
walls, is thus explained. In a specimen from Davis's Straits, in
Mr. A. Hancock's collection, most of the above characters are in an
intermediate condition; there are only a few external longitudinal
ribs on the parietes; and the terga have not purple apices. In Mr.
Cuming's collection there are some fine, brilliantly white specimens
(_without opercula_) from the coast of China; these have thin walls
and radii, and the walls are not longitudinally ribbed, but they are
not smooth: the orifice is not large, nor the shape of the whole
shell cylindrical. It is just possible that these latter specimens
may be a distinct and representative species, but I do not think so.