LEPAS CARETTA. Spengler. Skrifter, Naturhist. Selbskabet, Bd. 1, 1790, Tab. 6, fig. 4.
BALANUS CHELYTRYPETES. Hincks (!) sine descript., Annals of Nat. Hist., vol. 5, p. 333.
CORONULA SULCATA. Chenu. Illust. Conch., Tab. 1, fig. 1.
Shell globulo-convex, extremely massive and heavy; upper part worn, sub-striated: radii either not developed or very narrow: parietes without cavities extending up between the interrupted, radiating septa.
Hab.—West coast of Africa; northern Australia; common. Attached to, and generally imbedded in, the carapaces of turtles.
General Appearance.—Shell extremely strong, massive, heavy, broadly oval, globulo-convex, though sometimes depressed; dirty white: surface in the upper part always worn and disintegrated, hence finely striated; in the lower part a little rugged, slightly folded, and occasionally, in deeply imbedded specimens, much folded or ribbed. Orifice oval, not at all angular, rather exceeding in length one third of the basal diameter of the shell. Radii either not at all developed, or very narrow; but even in the former case the six lines of suture are plain; and in the latter case the radii lie at some depth beneath the surface of the shell. It is remarkable that the compartments are hardly ever arranged symmetrically, the rostrum and carina not facing each other exactly; and this holds good in specimens attached separately, without any apparent cause for this want of symmetry. The largest specimen which I have seen was 2.1 in basal diameter; and this, which was a steeply conical individual, was 1.1 in height; and therefore nearly twice as high as an ordinary large specimen of [C. testudinaria].
Structure of Shell and Radii.—The descending sheath and radiating septa are of very variable thickness, and have their basal edges finely dentated. The septa are not continuous, from the circumference to the sheath, in unbroken plates, but are irregularly divided into separate, often short portions, and even occasionally into mere points. The sheath differs from that of the other two species in having loopholes for the entrance of ribbons of corium only on the eight lines of suture, and not (with rare exceptions) in the middle of each compartment: this is evidently due to fewer filaments of corium being here sufficient to supply the less deep interspaces between the radiating septa; for in this species there are no flattened cavities or tubes running far up the shell. The inner lamina of the walls cannot be here distinguished, for a solid, flat, calcareous surface extends from the circumference, between the radiating septa, to the sheath. The sheath, had it not been from the light thrown on this part by the other species, would have certainly been mistaken for the inner lamina of the walls. The absence of the flattened cavities or tubes extending up the parietes, seems to be the least varying character; and serves to distinguish this species from those worn and massive specimens of [C. testudinaria], which have narrow and not-notched radii.
In specimens in which the radii are not developed, no vestige of the outer lamina can be detected, the lateral faces of the adjoining compartments being closely pressed together; but in specimens in which the radii have been developed and have grown, the outer lamina of course is present, and is extremely thick, with the growing edge having a branched and mammilated surface, as in [C. testudinaria], but with the external surface not pitted or notched as in that species. The inner portion of the radius, whether or not developed, has nearly the same appearance, consisting of rather thick transverse septa, branching from a central ridge, which is sometimes obscure.
The Alæ are remarkably little prominent, as least in those specimens in which the radii are not developed, so that Spengler seems to have thought that the structure of the shell was essentially different from that of [Balanus], which certainly is by no means the case. The edges of the alæ are very thick, nearly as thick as the inner portion of the radius.
The Opercular Valves hardly present any essential difference, compared with those of the other species; but the occludent margin of the scutum is apt to be more sinuous, and its rostral end blunter and squarer. The carinal end of the tergum is also squarer than in any common variety of [C. testudinaria]; the external furrow or spur, near the carinal margin, is very indistinct, and even sometimes is quite absent.