Compartments: their exterior appearance has been already described. The parietal tubes are not large; they are generally crossed by transverse septa in their uppermost part; but they are sometimes almost solidly filled up by dark shelly layers. The internal surface of the parietes is more or less plainly ribbed; in old specimens, however, it generally becomes smooth. The radii have their septa denticulated on both sides; and they are porose, that is, the interspaces between the septa are not filled up solidly. The radii generally extend from tip to tip of the adjoining compartments, that is, their summits are parallel to the basis; but in three not common varieties, viz., vars. intermedius, occator, and d’Orbignii (the former of which at least must, without the smallest doubt, be ranked as a mere variety), their summits are oblique. I have occasionally met with specimens of var. communis with oblique radii; and this is not very infrequent in young shells. Exteriorly the radii are generally smooth, but sometimes finely ribbed horizontally, owing to the projection of the septa. The alæ have their sutural edges smooth; their summits are usually parallel to the basis, but they are often much broken; in var. zebra, however, in every specimen which I examined, the summits were oblique. The sheath varies much in colour: in var. occator, and in a less degree in var. intermedius and var. d’Orbignii, the portion lining the rostrum and lateral compartments is much darker than the other parts of the sheath. The Basis generally has a thick, underlying, cancellated layer. Sometimes the basis (Pl. [1], fig. [b]) is irregularly cup-formed.
Mouth: labrum with four or six minute teeth: mandibles with five graduated teeth; inferior point more or less spinose. Maxillæ, either with or without a small notch, beneath the upper pair of spines; in the lower part there are two spines longer than those immediately above them. Cirri, the first pair has the rami unequal, in the proportion of about 19 segments in the longer ramus, to 16 in the shorter. The segments in the latter have their anterior surfaces very protuberant. The second pair is short, with the anterior surfaces of the segments protuberant. On the thorax (Pl. [25], fig. [1]), on each side, at the bases of third pair of cirri, there is a projecting membranous plate fringed with fine bristles. The three posterior pairs have their segments shield-shaped in front, generally bearing four pairs of spines, of which the lower pair is minute; between these pairs there are some minute spines. In some young specimens from the Cape of Good Hope, and in var. concinnus, I found six pairs of spines on the segments of the posterior cirri.
Geographical Distribution.—This species is extremely common over the whole of the warmer seas. It ranges from the Island of Madeira to the Cape of Good Hope, and on the west coast of America, from Monterey, in lat. 37° N., in California, to Peru. It is attached to rocks and sub-littoral shells, to floating timber, to kelp, and to Lepas anatifera. It is attached in wonderful numbers to ships’ bottoms arriving at our ports, from West Africa, the West Indies, the East Indian Archipelago, and China. It is generally associated with [B. amphitrite] and [amaryllis]. I have already stated that, on the bottoms of vessels, the different varieties are generally grouped together; and this makes me believe that they are local. In Mr. Stutchbury’s collection there are numerous specimens taken from a ship which first went to the west coast of Africa for guano, and then to Patagonia for the same object, and it was interesting to see the manner in which numbers of [B. psittacus], a Patagonian species, had become attached on the African B. tintinnabulum. The varieties from the west coast of America seem eminently peculiar; we there find var. coccopoma and concinnus; and a blueish, rugged variety, with peculiar opercular valves.
Geological History.—I have seen specimens in Mr. S. Wood’s collection from the Red Crag of England, which, though not accompanied by opercular valves, I cannot doubt belong to this species. The specimens named by Mr. Sowerby, in the ‘Mineral Conchology,’ as B. crassus, and which I have seen through the kindness of Mr. J. de C. Sowerby, also belong to this species. I further believe that a specimen in Sir C. Lyell’s collection, given to him by M. Dujardin under the name of B. fasciatus from Touraine, is likewise [B. tintinnabulum].
Varieties.
With respect to var. communis, I have nothing to remark. The second, var. vesiculosus (Pl. [2], fig. [1 h]), is confined to young specimens, and may, perhaps, be due to a want of calcareous matter. With respect to var. validus (Pl. [1], figs. [1 c], [1 f] infra), I may observe that some of the coarsest and strongest specimens which I have seen were said to have been attached to a surface of iron. I have seen two large lots of var. zebra ([1 g]), taken by Mr. Stutchbury, from the bottoms of ships, arriving from Bengal and China, and in both cases associated with var. communis, and in one case with var. coccopoma. I at first thought that this variety, zebra, was specifically distinct, but now I feel no doubt, that it is a mere variety; its body was in every respect identical with that of var. communis.
Nor have I any doubt that var. crispatus, of Schröter (Pl. [1], fig. h), is only a variety, although the scuta in some specimens have a peculiar appearance, externally like these valves in var. occator (Pl. [2], fig.[1 b]): the scutum is here broader and flatter than in var. communis, and the adductor ridge is very feebly developed, but we shall see how variable this ridge is in all the varieties: externally, the sharp, hood-like points formed by the upturned lines of growth, have a very remarkable appearance, from being arranged in quite straight radiating lines. This structure is evidently caused by the same tendency which produces on the walls the sharp, upturned, irregular points; but it is singular that the scuta are smooth in some specimens with very rough parietes; and, on the other hand, bristling with the symmetrically arranged, hood-like projections, in other specimens on which I could with difficulty detect only a few exceedingly minute points on the walls. In var. communis I have seen a few specimens with a slight tendency in the scuta to become striated longitudinally. The tergum in var. crispatus presents no difference from that in var. communis. Some of the roughest and best characterised specimens of var. crispatus appear to have come off copper-sheathed vessels.
I believe var. spinosus of Gmelin (Pl. [1], fig. i), has been correctly considered by me as a variety, but I have unfortunately seen only one set of specimens with their opercular valves preserved: these were attached to Lepas anatifera. The colour of the shell varies from reddish-purple to nearly white; the radii are sometimes quite white; the walls are slightly ribbed. The scuta in the above specimens, externally were smooth; the adductor ridge was rather more distinct from the articular ridge than in any other variety; and the terga rather more plainly beaked. The tubular, up-curved, calcareous spines sometimes occur only on one side of the shell, and often only in the lower part. These spines are often coloured brighter than the walls. Their presence cannot be accounted for (any more than the state of the scuta in the foregoing var. crispatus) by the nature of the surface to which they are attached; for I have seen one set attached to a large rugged specimen of [B. tintinnabulum], and another to the very smooth valves of Lepas anatifera. I believe that this form is almost always associated with var. communis, which is an argument that it is only a variety.
To var. coccopoma (Pl. [1], fig. d) I alluded in my introductory remarks as having so strongly the aspect of a distinct species. I possess a beautiful group, with a globulo-conical, smooth shell, of the finest rose colour, with a rather small, rounded orifice. These specimens were attached (mingled with [B. trigonus]) to Avicula margaritifera, from, as Mr. Cuming believes, Panama. I can never look at this set of specimens without doubting the correctness of the determination at which I have arrived. In the British Museum there are two sets of specimens taken off a vessel, on the west coast of South America, almost identical in external appearance with those in my possession, but rather more rugged. Mr. Stutchbury has sent me some specimens from a ship, direct from China, which are rather paler pink, and more striped, and come near to some ordinary varieties of [B. tintinnabulum]. The scuta (Pl. [2], fig. [1 f]) in the above three sets of specimens agree in having the adductor ridge more developed, and the pit for the lateral depressor muscle deeper than is usual. The tergum ([1 l], [1 o]) in most, but not in all these specimens, has a rather broader spur; and some of the specimens have the carinal portion of the basal margin considerably hollowed out; the spur, also, is placed nearer the basi-scutal angle than in ordinary cases. On the other hand, in Mr. Cuming’s collection, there are two specimens taken off a vessel, identical in external appearance with the foregoing, but which have scuta and terga in every character exactly as in var. communis; hence I am compelled to consider all these specimens as mere varieties.
Var. concinnus (Pl. [1], fig. e) is, perhaps, the most remarkable of all the varieties; I have seen three sets of specimens from the west coast of South America,—all identical in appearance, having longitudinally-ribbed walls, either rosy or of a dull purple, striped and freckled in a peculiar manner with white. I have, however, seen an approach to this colouring in some few specimens of var. communis; and the shell itself offers no other peculiarities. The scutum (Pl. [2], fig. [1 g]) resembles, in general shape, that of var. coccopoma; but the adductor ridge is here much sharper and more prominent; and the rostral depressor muscle, instead of being lodged in a little cavity formed by the folding over the occludent margin, has, in addition, a small plate on the under side, which tends to convert the pit into a tube. The tergum exactly resembles that of var. communis. The segments in the sixth cirrus bear six, instead of four, pairs of spines,—a circumstance which I have noticed only in some young specimens of var. communis, from the Cape of Good Hope. From these several peculiarities, until quite lately, I resolved to keep this form specifically distinct; but I have finally concluded that they are not sufficient. For firstly, I have seen a scutum in var. communis (Pl. [2], fig. [1 d]), with the adductor ridge nearly as sharp; and this ridge is always strongly pronounced in var. coccopoma; secondly, with respect to the plate for the rostral depressor muscle, although I have not seen this in any other variety, yet in [Bal. concavus] a closely analogous plate, situated in the lateral depressor cavity, is highly variable, and I am not willing to found a new species on one minute point of structure,—a structure which is variable in another species of the same genus.