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.
Neither the mouth nor cirri present any deviations from the generic
character.