LEPAS COLUMNA. _Spengler._ Skrifter Naturhist. Selbskabet, b. 1,
(1790), Tab. 6, fig. 6.
_Sutures, excepting during early youth, generally obliterated both
externally and internally: tergum with small pits for the attachment of
the depressor muscle._
_Hab._--New South Wales, Tasmania, New Zealand; extremely common;
attached to littoral shells and rocks; often associated with
_Chthamalus antennatus_ and _Elminius modestus_; and in New Zealand,
often thickly coating _Elminius plicatus_.
I have identified, with some doubt, the present species with the _Lepas
columna_ of Spengler, obtained from Otaheite, as no description is
given by him of the opercular valves, and more especially as Spengler's
specimens were an inch in height and seven lines in width, which is
much larger than any of the many specimens seen by me: from Spengler's
clear description of the structure of his shell, it evidently belongs
to the present genus.
_General Appearance and Structure of Shell._--The sutures separating
the four compartments are generally, excepting at an early age, quite
obliterated, both internally and externally, the shell in this case
consisting of a single piece, with its summit and opercular valves
always much worn. Occasionally the sutures are preserved, and then
the four compartments are seen to be of nearly equal sizes. The
orifice is always broadly oval, with the carinal end the broadest;
and it often approaches closely to circular. The upper part of the
shell is frequently steeply conical, with the lower part spreading
and folded; sometimes deeply folded. Very young shells are apt to
be remarkably smooth. The radii appear never to be developed: the
inside of the shell is smooth. The colour is either blackish-green
(this being the tint of the corium lining the sack), with the upper
part gray from disintegration; or the lower part is brown, from
the investing membrane, the shell itself being pale coloured. This
species seems particularly liable to grow crowded together; often
covering rocks and shells with a honey-combed layer. The basal
diameter of some of the largest specimens was .3 of a inch. In Mr.
Cuming's collection, however, there is an Australian specimen .55
in diameter and .3 in height, which is, moreover, remarkable from
the projecting, extremely rugged, overlapping, dark-coloured layers
of growth, which surround the lower part of the shell: we have seen
that Spengler's specimens, said to have come from Otaheite, are even
broader and considerably higher.
_Scuta_: from the disintegration which the valves have undergone, the
scuta and terga are externally seen to be locked together by a deeply
sinuous articulation. The _Scuta_ have a wide articular furrow and a
very prominent articular ridge; but the exact outline of these parts
varies greatly, very much as in the genus Chthamalus.
The _Terga_ are very narrow, with the under surface channelled: the
attachment of the depressor muscle offers the only peculiarity,--the
muscle being attached to four or five little pits, placed
transversely to the longer axis of the valve; the septa between these
little pits evidently answering to the crests as usually developed.
_Mouth._--The crest of the labrum is hairy, and slightly bullate.
The palpi are rather small, with long spines at their ends. The
mandibles have four (sometimes five) teeth, with the inferior portion
pectinated. The maxillæ are notched.
_Cirri._--The first pair presents no remarkable character. The second
and third pairs are subject to extreme variation, as in _Chthamalus
antennatus_ and _Tetraclita porosa_. In all the specimens, the
anterior ramus of the second cirrus is short, with all the segments
thickly covered with bristles; it is the posterior ramus which varies
so much in relative length and in the arrangement of the bristles;
but in no case are all the segments clothed with bristles as on
the anterior ramus, and as is normally the case with all sessile
cirripedes. In some specimens from New Zealand, the anterior ramus
having only five segments, the posterior ramus was twice as long,
having sixteen segments, with the bristles arranged in circles,
but standing rather thicker together on the basal segments. In a
Tasmanian specimen, the posterior ramus was only a little longer than
the anterior ramus, and the spines were arranged in regular pairs (as
on the three posterior pairs of cirri) on all the segments, excepting
the few basal ones, on which they were more crowded: a nearly similar
arrangement occurred in some other specimens from unknown localities,
excepting that the rami were of nearly equal length. In the third
cirrus, in all the specimens, the anterior ramus has three or four of
its basal segments much broader than the upper segments, and thickly
clothed with spines (as is the case with one species of Chthamalus,
viz. _C. intertextus_) all the other segments having regular pairs
of spines. The posterior ramus of the third cirrus varies in being
either much longer than, or only equal in length to, the anterior
ramus; in the former case (in the New Zealand specimen) the spines
were arranged in circles, giving an antenniformed structure to the
ramus; and in the latter case they were arranged in regular pairs.
In Mr. Cuming's great Australian specimen, there was a further
peculiarity, in the presence on the posterior cirri of a tuft of
intermediate spines between the main pairs; and, in there being on
those segments, which are thickly covered with spines, certain very
large spines, doubly pectinated, with the pectinations elbowed,
closely like the spines met with on the cirri in certain species of
Pollicipes. Finally, the segments in the three posterior pairs of
cirri support five or six pairs of main spines; the dorsal surfaces
of the segment are rough and hairy.
_Branchiæ_, rudimentary; consisting of a small, simple, tongue-formed
fold, projecting about 1/100th of an inch. Ova, 16/2000ths of an inch
in length.