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.