ELMINIUS PLICATUS. _J. E. Gray._ Appendix to Dieffenbach's Travels in
New Zealand, p. 269, 1843.
_Shell deeply folded longitudinally, corroded, coloured in parts
orange: radii very narrow, with their edges sinuous, and slightly
dentated: scutum having an adductor ridge._
_Hab._--New Zealand; New South Wales(?). Attached to rocks, often
coated by _Chamæsipho columna_; Mus. Brit. and Cuming.
_General Appearance._--Shell tubulo-conical, or conical, rarely
depressed; strong, rugged, coloured in parts bright orange; deeply
plicated longitudinally, but with the upper parts corroded and
smooth. Orifice large. The sutures are indistinct and almost
obliterated; the radii, when most developed, are narrow. Some
specimens have their whole surface deeply corroded; in which case
they are finely striated longitudinally, or pitted, and are of a
gray or brown colour. The largest specimens are one inch in basal
diameter, but one depressed specimen was 1.3 in diameter; another was
rather under one inch in diameter, and one inch in height.
_Scuta_; beginning with the common tubulo-conical and not much
corroded specimens, the valve (fig. 2 _c_) is moderately elongated,
but in a rather variable degree. A prominent adductor ridge runs,
from a little above a middle point of the basal margin, along
the slightly prominent articular ridge: the articular furrow
is moderately wide. There are distinct crests for the lateral
depressores. In the conical, corroded specimens, the scuta (fig. 2
_e_) are considerably broader, with the articular ridge much more
prominent, and the furrow wider: in one such specimen, there were
crests for the rostral depressor muscle.
The _Terga_, in the commoner variety, resemble those of _Tetraclita
porosa_; the spur adjoins the basi-scutal angle of the valve: the
articular ridge is moderately prominent, and the furrow moderately
deep. The valve is beaked, with an unusually large internal tube
for the thread of corium: the beak, however, is often worn away. In
the depressed much corroded specimens, the terga (fig. 2 _f_), like
the scuta, are broader and shorter than in the commoner variety;
and the spur more especially is broader. The scutal margin is much
more widely inflected, and the articular ridge much more prominent;
consequently the articular furrow is much deeper.
_Structure of the parietes and radii._--The orange or yolk-of-egg
colour, which is so conspicuous a character in the present species,
is due to a layer of shell between the inner and outer lamina, and
is exposed only by the corrosion of the latter. Hence the very base
of the shell is not of this colour; nor are the uppermost and still
more deeply corroded portions, for here the orange-coloured layer has
been removed. The sheath is orange-coloured, and the operculum, to a
certain extent, is similarly tinted. The epidermis on the parietes,
where preserved quite close to the basis, supports remarkably strong
spines, about 1/100th of an inch in length. The basal internal edges
of the walls are rather coarsely striated with irregular short ridges
and sub-cylindrical points; and the walls in most of the specimens
are regularly and deeply folded, which, with the little ridges, gives
the appearance represented in fig. 2 _b_, Pl. 12. I have stated,
under the Genus, that in the corroded and depressed specimens, the
walls are rendered extremely thick by the inward production and
upward extension of these same ridges and points; the under surface
of the shell acquiring almost the appearance of _Chelonobia caretta_.
The Radii are often not developed, even the sutures being obscure;
when most developed, they are narrow, with the outer lamina along the
growing edge sinuous, giving to the sutures a crenated appearance.
The sinuosities on the growing edge generally send inwards short
ridges or septa, like those on the sutural edges of the radii in most
Balanidæ, but of which there is no trace in the other species of
Elminius. In very minute, colourless specimens, about the 1/20th of
an inch in diameter, the radii are quite smooth-edged. The alæ have
their edges strongly crenated. The lower edge of the sheath depends
freely.
_Mouth_: the labrum shows some tendency to be bullate; the notch is
broad and shallow: the palpi have a thick brush of bristles on their
inner sides. The mandibles have four or five teeth. In the maxillæ,
the upper spines above the broad notch, are very strong. In the outer
maxillæ, the two lobes are widely separated.
_Cirri_: in the first pair, one ramus is about one fifth longer
than the other. In the third pair, the posterior ramus is one
fourth longer than the anterior ramus, and its terminal segments
are tapering, each having a single circle of bristles: the other
segments, and those of the shorter ramus, support many coarsely
pectinated spines. In the sixth cirrus, the segments are protuberant
in front, and carry four pairs of stout spines, with a tuft of fine
bristles between them.
_Affinities._--This species differs considerably from the first two
of the genus. In several characters it approaches nearer than the
other species to Tetraclita, especially to _T. porosa_;--namely,
in the scutum having an adductor ridge and crests for the lateral
depressores, in the whole form of the tergum, in the thick walls
liable to much corrosion, in the narrow radii, and in their edges,
as well as those of the alæ, being crenated; and, lastly, in the
character of the cirri, more especially of the third pair, with
its coarsely pectinated spines. It also approaches, in all its
characters, _Balanus imperator_ and _flosculus_.