BALANUS CONCAVUS. _Bronn._ Italiens Tertiär-Gebilde (1831) et Lethæa
Geognostica, b. ii, s. 1155 (1838), Tab. 36, fig. 12.[94]
---- CYLINDRACEUS, _var._ c. _Lamarck._ Animaux sans Vertèbres
(1818).
LEPAS TINTINNABULUM. _Brocchi._ Conchologia Sub-Appen., t. ii, p. 597
(1814).
[94] I suspect that _B. pustularis_, _miser_, and _zonarius_, all
figured by Münster, in his 'Beiträge,' b. iii, Tab. 6, may be this
species.
_Shell longitudinally striped with white and pink; or dull purple;
sometimes wholly white. Scutum finely striated longitudinally;
internally, adductor ridge very or moderately prominent._
_Hab._--Panama; Peru; S. Pedro in California; Philippine Archipelago;
Australia. Mus. Brit., Cuming, Stutchbury, Aug. Gould.
_Fossil_ in Coralline Crag, England; Mus. Brit., S. Wood, Bowerbank,
Lyell, J. de C. Sowerby, Tennant. Sub-Appennine formations, near
Turin, Asti, Colle in Tuscany, Mus. Greenough, &c. Tertiary beds,
near Lisbon, Mus. D. Sharpe and Smith. Bordeaux (?) Mus. Lyell.
Tertiary beds, Williamsburg; and Evergreen, Virginia, Mus. Lyell.
Maryland, Mus. Krantz. Recent formations[95] near Callao, Peru, Mus.
Darwin. Red Crag (Sutton) Mus. S. Wood.
[95] I procured this specimen from the Island of S. Lorenzo, off
Callao; it was imbedded, together with seventeen species of recent
shells and with human remains, at the height of eighty-five feet.
This species has caused me much trouble. Looking first to the recent
specimens, I examined several from Panama and California, which,
though differing greatly in colour, resembled each other in their scuta
having the adductor ridge extremely prominent, and in having (Pl. 4,
fig. 4 _a_), an almost tubular cavity for the attachment of the lateral
depressor muscle,--characters which at first appeared of high specific
value; but I soon found other specimens from Panama in which these
peculiarities were barely developed. I then examined a single specimen
from the Philippine Archipelago, resembling in external appearance one
of the Panama varieties, but differing in the scuta being externally
strongly denticulated in lines instead of being merely striated,--in
the adductor ridge being far less prominent,--and in the spur of the
tergum being broader and more truncated; I therefore considered this
as a distinct species. I then examined a single white rugged specimen
from the coast of Peru, which differed from the Philippine specimen
in the shape of the well-defined denticulations on the scuta, and in
some other trifling respects, and in the segments of the posterior
cirri bearing a greater number of spines; with considerable doubt, I
also named this as distinct. But when I came to examine a large series
of fossil specimens from the Coralline Crag of England, from northern
Italy, from Portugal, and from the southern United States, I at once
discovered that the form of the denticuli on the scuta was a quite
worthless character,--that in young specimens the scuta were only
striated,--that the prominence of the adductor scutorum ridge and the
depth of the cavity for the lateral depressor muscle varied much (as
in the case of the recent specimens), owing apparently to the varying
thickness of the valve,--that in the terga the spur varied considerably
in length and breadth, the latter character being in part determined
by the varying extent to which the edges of the longitudinal furrow
are folded in,--and lastly, that in young specimens the basal end of
the spur is much more abruptly truncated than in the old. Hence I have
been compelled to throw all these forms, originally considered by me
as specifically distinct, into one species. I must repeat that this
considerable variation in the prominence of the adductor ridge, and in
the depth of the pit for the lateral depressor muscle--the pit in some
cases becoming even tubular--is a very unusual circumstance.
With respect to the fossil specimens[96] from the above-stated several
distant localities, I consider them as certainly belonging to one
species, though varying considerably in several points of structure.
When compared with the recent specimens, they differ from them in often
attaining a considerably larger size; in the parietes being often, but
not always, longitudinally ribbed; and in the radii often having more
oblique summits. On the other hand, considering the many points of
identity between the fossil and the recent specimen, I have concluded,
without much doubt, that they ought all to be classed together. I may
remark that, in the Coralline Crag specimens, the spur of the tergum
(Pl. 4, fig. 4 _d_), is unusually long and narrow; it is broader and
shorter in the Italian specimens (4 _e_), and variable in this respect,
in the United States specimens; the scuta of the Lisbon specimens
are remarkable for the greater prominence of the adductor ridge, and
for the depth of the lateral depressor cavity. Some of the specimens
from all the several localities are identical with the recent ones
from the coast of Peru. The walls of the shell in the Coralline Crag
specimens, are generally ribbed longitudinally. I have entered into
the above particulars, on account of, in the first place, its offering
an excellent example how hopeless it is in most cases to make out the
species of this difficult genus without a large series of specimens;
secondly, as showing how the characters alter with age; and thirdly, as
a good instance of the amount of variation which seems especially to
occur in most of the species which have very extensive ranges.
[96] These will be fully illustrated in the monograph on the Fossil
Balanidæ, to be published by the Palæontographical Society.
Some of the pink-striped Panama varieties, though having a somewhat
different aspect, can be distinguished from certain varieties of _B.
amphitrite_ only by their scuta being longitudinally striated,--a
character in this species variable in degree, and in most cases of
very little value. Some of the other recent varieties are sufficiently
distinct from _B. amphitrite_; and the great fossil Coralline Crag
specimens, which stand at the opposite end of the series of varieties,
with their ribbed walls, very oblique radii, and coarsely striated
scuta, are extremely unlike _B. amphitrite_. With respect to the
nomenclature of the present species, I have little doubt that I have
properly identified the Italian fossil specimens with _B. concavus_ of
Bronn, who has given a very good figure of this species in his 'Lethæa
Geognostica;' it must, however, be confessed that the longitudinal
striæ on the scuta are not there represented. Considering the large
size and frequency of this species in Europe and in the United States,
it has probably received several other names, besides the two incorrect
synonyms, quoted at the head of this description. I should add that
the true _B. cylindraceus_ (not _var._ C) of Lamarck, according to the
plate given by Chenu in his 'Illust. Conch.,' is the _B. psittacus_ of
South America. I have seen in collections specimens of _B. concavus_
labelled as _B. tulipa_ of Poli (_B. tulipiformis_ of this work),--a
very natural mistake, without the opercular valves be carefully
examined.
_General Appearance._--Shell conical, often steeply conical; orifice
rather small, with the radii narrow, and generally in the fossil
specimens very oblique; surface generally smooth, sometimes rugged,
and in the coralline crag specimens generally ribbed longitudinally,
the ribs being narrow. Colour various, either dull reddish-purple
with narrow nearly white, or wider dark longitudinal bands; or,
again, pale rosy-pink with broad white bands; or lastly, wholly
white. The radii are either darker or paler than the parietes. The
opercular valves are either dark purple or nearly white. Pale pink
and white stripes are visible on some of the Italian and Portuguese
tertiary specimens; and in most of the fossils the sheath is tinged
dull red.
_Dimensions._--The largest actually recent specimen which I have
seen, from the Philippine Archipelago, had a basal diameter of 1.2
of an inch; the Peruvian pleistocene specimen is 1.7 in diameter;
specimens from the crag and from the Italian deposits, however,
sometimes slightly exceed two inches in basal diameter, and three in
height.
_Scuta_: these in young and moderately-sized specimens are striated,
sometimes very faintly, but generally plainly, causing the lines of
growth to be beaded; but often, in large and half-grown specimens,
the lines of growth are extremely prominent, and being intersected by
the radiating striæ, are converted into little teeth. As the striæ
often run in pairs, the little teeth frequently stand in pairs,
or broader teeth have a little notch on their summits, bearing
a minute tuft of spines. In very old and large specimens, the
prominent lines of growth are generally simply intersected by deep
and narrow radiating striæ. In one case, a single zone of growth in
one valve was quite smooth, whilst the zones above and below were
denticulated. The valve varies in thickness, which I think influences
the prominence of the lines of growth and the depth of the striæ.
These striæ often affect the internal surface of the basal margin,
making it bluntly toothed. The articular ridge is rather small,
and moderately reflexed: the adductor ridge (as already stated,)
varies remarkably; in most of the Panama specimens, it is extremely
prominent, and extends down to near the basal margin; in other
specimens it is but slightly prominent, especially in some of the
fossil specimens from Virginia. The cavity for the lateral depressor,
also, varies greatly; it is often bounded on the side towards the
occludent margin by a very slight straight ridge, which occasionally
folds a little over, making almost a tube; this, at first, I thought
an excellent specific character, but far from this being the case,
the cavity often becomes wide, quite open, and shallow.
_Terga_, very slightly beaked; the surface towards the carinal end of
the valve, in some of the fossil specimens, is very slightly striated
longitudinally. There is either a slight depression, or more commonly
a deep longitudinal furrow, with the edges folded in and touching
each other, extending down the valve to the spur, and causing the
latter to vary in width relatively to its length. When the furrow
is closed in, the spur is about one fourth of the entire width of
the valve, and has its lower end obliquely rounded, and stands at
about its own width from the basi-scutal angle: when there is only
a slight depression and no furrow (as is always the case with young
specimens), the spur is broader, equalling one third of the width
of the valve, with its lower end almost truncated, and standing at
about half its own width from the basi-scutal angle. But the absolute
length of the spur, also, varies considerably; it is often very long,
compared to the whole valve. The basal margin on the carinal side
is sometimes slightly hollowed out; when the furrow is closed, this
latter side slopes towards the spur. Internally, the articular ridge
and crests for the tergal depressor muscle are moderately prominent.
_Parietes_, the longitudinal septa sometimes stand near each
other, making the parietal pores small. The _radii_ have oblique
summits, but to a variable degree; their septa are unusually fine,
and are denticulated on their lower sides; the interspaces are
filled up solidly. The _alæ_ have their summits very oblique,
with their sutural edges nearly or quite smooth. In most of the
fossil specimens, and slightly in some of the recent specimens, the
surface of the sheath presents an unusual character, in a narrow,
longitudinal, slightly raised border, running along the sutures, on
the carinal side of each compartment.
_Basis_ thin, porose; sometimes with an underlaying cancellated layer.
_Mouth_: labrum with six teeth: mandibles with the fourth and fifth
teeth small, either sharp, or blunt: maxillæ with a straight edge,
or with the inferior part slightly prominent. _Cirri_ with the rami
of the first pair unequal by four or five segments: the segments in
the shorter ramus are extremely protuberant. The segments in the
second cirrus only moderately protuberant: but all the specimens were
in bad condition, and it appeared as if, in the Panama specimens,
the segments of the second cirrus were more protuberant than in the
Philippine Island specimens. In the posterior cirri there are from
three to five pairs of spines on each segment: even amongst the
Panama specimens some had three and some four pairs, and a white
Panama specimen had five pairs of spines.
All the recent specimens which I have seen, were, with one exception,
attached to various shells and crabs, and to each other. The Peruvian
specimen was associated with _B. flosculus_. The tertiary specimens are
often congregated together into great masses. Including the recent and
fossil specimens, this species encircles the globe. During the miocene
period it seems to have been the commonest existing sessile cirripede;
now, it does not appear to be common, excepting, perhaps, at Panama:
Mr. Cuming procured only one specimen from the Philippine archipelago.