---------- LAMARCKII. Leach. Encyclop. Brit. Suppl., vol. 3 (1824), Pl. 57.
CORONULA TUBICINELLA. De Blainville. Dict. des Sciences Nat., tom. 32, Pl. 117, fig. 5 (1824).
[127] It may be observed that I have here broken through the great law of priority; for it appears to me too grossly incorrect to retain the specific name either of major or minus in a genus including a single species. Lamarck himself seems to have been of this opinion, by giving, in 1818, the new specific name of balænarum; but Shaw’s name of trachealis has the clear right to priority, if major or minus be rejected.
General Appearance.—Shell elongated, sub-cylindrical, with the upper end rather wider than the lower, and therefore widening in a direction the reverse of that usual with sessile cirripedes. The shell is often a little bent to one or the other side: it is surrounded by from two or three to about ten very prominent, strong, blunt ridges or belts, placed at rather irregular distances from each other. The surface is finely striated longitudinally. The six compartments are of nearly equal sizes and shapes. In full-grown specimens the parietes are not wider at the base, and often they are even a little narrower, than at the summit of the shell: in young specimens the parietes do widen a little downwards. The radii are narrow; but in young specimens they are proportionably much broader (Pl. [17], fig. [3 b]) than in old specimens. The whole compartment, including the radius and wall, is always a little wider at the summit than at the base, in accordance with the shape of the whole shell. The operculum consists of four nearly equal-sized, similar valves, projecting above the upper end of the shell, which is always broken and jagged: the valves are united to the sheath by a very thick, much folded membrane. The aperture leading into the sack is bordered by very prominent lips, projecting above the opercular valves; the latter have their upper layers always scaled off. The shell is imbedded in the whale’s skin up to the level of its operculum. The largest specimen which I have seen was barely one inch (.95) in diameter at the summit, and 1.5 in length; the longest specimen which I have seen scarcely attained a length of one inch and three quarters.
Structure of the Shell.—The parietes are thin, and if the sheath (which extends to near the basis) be removed, they are rendered extremely thin. They are formed by an outer and inner lamina, united by fine longitudinal septa, projecting at the basis beyond the laminæ. The pores thus produced (which in a transverse section are oblong in outline), run up to the summit of the shell, and are not filled up by shelly matter; but I presume that the included tubular threads of corium are protected, at the broken upper end of the shell, by transverse membranous septa. The outer lamina of shell, as in [Coronula], is formed, though obscurely, by the union of ledges projecting from the longitudinal septa. The circular prominent belts, surrounding the shell, are formed by the longitudinal septa, at certain, irregular and rather distant periods, growing outwards; the wall at each belt being increased to nearly twice its thickness in other parts. At each belt the threads of corium within the parietal pores lend off minute branches to supply the thickened wall. These belts, which continuously surround the shell, correspond (as is best seen in young specimens), with the little knobs or beads, which, in [Coronula] (Pl. [16], fig. [4]), rise separately, and not quite regularly, on the longitudinal parietal septa, and which, I believe, are formed at every successive period of growth; here they are much larger, stand in straight transverse rows, become confluent, and are formed only at occasional intervals. The whole external surface of the shell is covered by membrane, stronger and more persistent than is usual with most cirripedes.
Internally the sheath extends almost to the basis of the much elongated shell, and terminates in a slight shoulder: it is divided as in common [Balanidæ], and differently from in [Coronula], into zones of growth, but these are very broad; at the upper end of the shell, which, as will hereafter be explained, is always breaking away, the sheath readily yields along the oblique planes, which separate the zones of growth and dip outwards: a similar but less strongly marked structure occurs in [Platylepas], and in no other genus. We shall presently see that the sheath presents a much more anomalous character, in being lined down to its basal edge by the innermost and last-formed layers of the opercular membrane.
Radii.—The radii are narrow. The belts which surround the shell are prolonged, with slightly diminished prominence, across the radii, their formation being simply due to the radii being here thicker than in other parts. It can be seen more plainly in [Tubicinella], than in other [Balanidæ], that the membrane externally investing the shell, splits along the radii during the diametric growth of the shell, and is continually repaired and added to along these lines by new longitudinal slips of membrane. The radius consists (as usual) of an inner and outer lamina, which latter does not extend quite to the line of suture—a slightly gaping fissure being thus left. The two laminæ are connected by septa, which are not denticulated, but near the outer lamina bi- or tri-furcate, and the ends of the branches thus formed spread out, forming a sort of outer scalloped lamina, in advance of the true outer lamina. The fine threads of corium running between these septa, do not spring, as in all common cirripedes, from a fillet of corium occupying the actual suture, but from two nearly circular threads of corium occupying two tubes, which run along the line of junction between the radius and the compartment whence it springs. In [Coronula] alone we have a nearly similar structure; for the fine threads of corium occupying the proper radius, spring from a single very minute tube (Pl. [16], fig. [7], d′), occupying the same position with the two tubes in [Tubicinella]. I may further add, that the structure of the proper radius in [Coronula] is precisely the same as here just described, but being on so very minute a scale, I did not there describe it so carefully as I have here done.
Alæ: these are only remarkable from their extreme thinness; for they are not thicker than the inner lamina of the radius. Their sutural edges are quite smooth. Forming part of the sheath, they extend down close to the basis of the shell; where, instead of, as in general, ending abruptly in a rectangular shoulder, they slope off into their own compartment.
Basis.—The basal membrane is complicated, owing to the shell, when full-grown, barely, or not at all, increasing in diameter, and, in consequence, membrane after membrane, each with its own cement-ducts attached to it, are thrown down one nearly over the other. In the [Introduction] (p. [143]—Pl. [28], fig. [3]), I have fully described the cementing apparatus, which is very curious from one of the ducts always having a loop with two spurs projecting from it. The basal membrane does not equal in diameter the base of the shell, for the membrane externally covering the walls is inflected inwards all round for a considerable width, and is then united to the basal membrane: in [Coronula], the basal membrane extends only under the internal cavity of the shell, and not under the folded walls, and therefore presents a somewhat analogous structure.