LEPAS BALÆNARIS. _Gmelin._ Systema Naturæ (1789).
---- ---- _Chemnitz._ Conch., vol. 8, Tab. 99, fig. 845, 846 (1785).
BALANUS ---- _Bruguière._ Encyclop. Method., Pl. 164, fig. 13-18
(1789).
CORONULA ---- _Lamarck._ Annales du Museum, vol. 1, Tab. 30, fig. 2-4
(1802).
---- ---- _Chenu._ Illust. Conch., Plate, fig. 1 and 4.
---- ---- _De Blainville._ Dict. des Scien. Nat., 1818 and 1824,
Tab. 117, fig. 3, 3 _a_.
_Shell much depressed, with longitudinal flattened ribs, having simple
edges; orifice rounded-hexagonal: radii very thick, almost equalling
the shell in thickness: opercular valves four._
_Hab._--Attached to whales in the Southern Ocean.
Having described, under the genus, in so much detail the structure of
the whole shell, it will be sufficient here to point out the characters
by which this species differs from the others.
_General Appearance._--The shell is generally much depressed, though
sometimes, in large specimens, from the turning in of the basal
edges, a considerable degree of convexity is acquired. The radii
are moderately wide, and give a star-like appearance to the shell.
The surface of the whole upper part of the shell is smooth; the
broad and much flattened ribs (_i. e._ the terminal, transverse
loops of the folded walls) of which each compartment is formed,
generally divide at a short distance from the apex. The close sutures
separating these ribs are straight, and not finely serrated, by which
character alone this species can at once be discriminated from the
others. The surface, when closely examined, is found to be finely
striated longitudinally, and is transversely crossed, chiefly in
the lower part, by minutely beaded growth-ridges. The orifice is
rounded-hexagonal, and is small compared with the whole shell; it is
also smaller than the basal edge of the internal cavity of the shell;
consequently the whole basal edge cannot be seen through the orifice
from one point of view,--the operculum of course having been removed.
An unusually large specimen was 2.75 of an inch in diameter; this
individual was one of the more convex varieties, and yet its entire
thickness, from top to base, was only .9 of an inch.
_Operculum._--Having described, under the genus, the general
structure of the opercular valve, I will here only add a few details
on their shape. They are small compared with the whole extent of
the opercular membrane. The scuta (Pl. 15, fig. 2 _b_, scutum to
the left) stand near each other at the rostral end of the aperture
leading into the sack, with their two rostral ends united by the
yellowish-brown, longitudinally plicated, horny membrane, described
under the genus. The terga (fig. 2 _b_) stand a little apart from
the scuta, on the sides of nearly the middle of the sack-aperture.
The lips are protuberant and moderately developed all round. The
scuta are elongated, and a little curved; including the upper
imbedded portion, they are almost sub-triangular: but the under
growing surface is much elongated, nearly flat, with the two ends
of nearly the same width, truncated and rounded. The _Tergum_, in
rather small specimens is, if the upper imbedded portion be included,
sub-triangular, with the growing surface oval, and between one third
and one half of the length of the scutum; but in large specimens,
the tergum becomes style-formed, lying parallel to the tergal margin
of the scutum, with the growing surface proportionally much smaller,
and not above one fifth of the length of the growing surface of
the scutum. Hence we see some tendency in the tergum to become
rudimentary, as it is in the next species. The brown, horny, plicated
substance in which the terga are imbedded, extends considerably
beyond the valves themselves.
_Structure of the Shell and Radii._--I have already so fully
discussed this subject, that I will here only enumerate the points in
which this species differs from _C. diadema_ and _reginæ_:--Firstly,
the more symmetrically folded walls (Pl. 16, fig. 5), new folds
arising on both sides of all six sutures. Secondly, the inner ends of
the folded walls, which surround the internal cavity, being almost
square, but with their angles rounded; their inner ends descend some
little way beneath the basal edge of the sheath, as low, or lower,
than the circumference of the shell. Thirdly, the external lines of
junction between the transverse terminal loops being smooth or not
serrated. Fourthly, these loops being flatter towards the outside,
and being internally filled by septa (Pl. 15, fig. 2 _a_); tubes
being thus formed larger than the proper parietal pores. Sixthly, the
sutural edges of the compound radii (Pl. 16, fig. 3) being very much
broader in the inner and upper part of each compartment than in the
outer and lower part; for in the inner and upper part they stretch
from the outside of the shell to the sheath, so that the alæ rest on
them, and hence no large open cavity is left between the radii and
alæ; in the inner and upper part, also, the radii extend down nearly
to the basal edges of the folded walls. The septa, of which the radii
are formed, stand further apart than in _C. diadema_ and _reginæ_.
Seventhly, the alæ are only 1/5th or 1/6th of the thickness of the
radii, whereas in the two other species they are very much thicker,
being nearly as thick as the radii: the alæ are also here (fig. 3,
_a′_) squarer than in those two species, that is, their basal margins
are not so short compared with their upper margins; their edges
present, also, a slightly different structure. Eighthly, the basal
edge of the sheath does not here project freely, and does not descend
quite so close to the basal membrane.
_Mouth._--The palpi are furnished with a row, extending along the
whole basal exterior margin, of very long upwardly pointing spines;
on their upper edges there is a brush of small spines. The edge of
the labrum is clothed with extremely fine spines, and is furnished
with a few minute teeth. The mandibles have four teeth, and the lower
end is broadly rounded and coarsely spinose: the second and third
teeth are double at their points, and between the second and third,
and again between the third and fourth, there is a small intermediate
tooth.
Regarding the _Cirri_, I have nothing especial to remark.
_Geographical Distribution._--I have examined nine sets of specimens,
having localities attached to them: three from off New South Wales;
two off the Cape of Good Hope; two from the west coast of South
America; and two marked only "South Sea." Hence I am led to conclude
that this species is confined to the southern hemisphere, or if it
extends into the northern hemisphere, it is probably only in the
Pacific Ocean. I do not believe (though so stated in some works) that
this species occurs on the shores of Europe. It seems often to be
associated with Tubicinella. Some specimens thus associated, sent by
Mr. Bennett to Professor Owen, were said to have been attached to the
_Balæna australis_.