CONIA RADIATA.[112] _De Blainville._ Dict. Sc. Nat., 1816-1830, Pl.
164, fig. 5, 5 _a_, (sine descript.)
---- LYONSII. _G. B. Sowerby._ Genera of Recent and Fossil Shells,
Plate, 1823, (sine descript.)
[112] The synonymy of this species is complicated. De Blainville
gives no description under the article Conia, published in 1818, or
in the vol. published in 1822; but I believe, from the figures of
the opercular valves, that I have correctly identified this species
with his _C. radiata_. Mr. Sowerby gives no description of _C.
Lyonsii_, or any figure of the opercular valves, but his drawing
of the shell is much better than de Blainville's, and I believe
it is the same species. Whether de Blainville's or Sowerby's
plate appeared first I cannot ascertain. In the second edition of
Lamarck, _Conia radiata_ of Blainville is given as a synonym to
_Balanus radiatus_ of that work; but this is quite erroneous. I
may add that if de Blainville's name does not apply to the present
species, it must to _T. cœrulescens_, and as the latter is the
older name it will be permanent. In this case, _T. radiata_ might
be allowed to stand as my own name, considering that Mr. Sowerby's
figure is imperfect and is not accompanied by any description.
At first I thought that the present species might be the _Lepas
mitra_ of Spengler, ('Skrivter af Naturhist. Selskabet,' 1790,
Tab. 6, fig. 5), but the parietes are not described as porose;
and the folds on the walls are too broad; on the other hand, his
description of the opercular valves makes me think this may be the
same species.
_Shell white, with numerous approximate longitudinal ribs: radii broad,
with their summits slightly oblique, internally porose: tergum with the
articular ridge extraordinarily prominent, with the spur not joined to
the basi-scutal angle._
_Hab._--West Indies, adhering to _Balanus eburneus_ and to _Lepas
anserifera_. New South Wales, adhering to _Tetraclita porosa_.
Attached to _Balanus tintinnabulum_, on a ship's bottom from Sumatra;
not rarely attached to _Balanus tintinnabulum_ on ships' bottoms;
Mus. Brit., Stutchbury, and Cuming.
_General Appearance._--Shell white, rather steeply conical, with
numerous, approximate, rather narrow, longitudinal, rounded ribs on
the walls: in a specimen half an inch in diameter, there were from
eight to twelve ribs on each compartment. The outer lamina of shell
seems always well preserved. Orifice rounded, trigonal. Radii white,
smooth, broad, with their summits only slightly oblique. I have
seen one specimen 1.2 in basal diameter, but quarter of an inch is
a common size, and very young specimens are unusually frequent in
collections.
_Scuta_ broad, externally not striated longitudinally. The articular
ridge is prominent, and the furrow deep, but not in so great a
degree as in _T. cœrulescens_. The adductor ridge is only slightly
prominent; it extends upwards only a little way above the lower end
of the articular ridge, and does not form with the latter a cavity.
There are no crests for the rostral depressor muscle, but there is a
little pit, formed by the folding over of the occludent margin.
_Terga._--These valves, when articulated with the scuta (fig. 5 _b_),
project above them to an extraordinary degree, and are separated
from them by a deep, fissure-like hollow, caused by the remarkable
prominence of the articular ridge of the terga. The upper part of
the tergum is not beaked, and does not project freely much above the
sack. The valve is large; externally there is a rounded longitudinal
furrow. The tergal margin is broadly inflected. The articular furrow
is deep, and the articular ridge far more prominent than in any other
sessile cirripede, for it projects, as measured from the outside
surface, more than half the width of the valve; and consequently
the valve, when viewed vertically from above, almost appears as if
formed by the union of three plates, viz., the articular ridge, and
the outside surface on each side of the spur. The spur is of moderate
width, with the corners rounded: it is placed near, but not close to
the basi-scutal angle, so that there is on this side a small portion
of basal margin, forming nearly a straight line with the margin on
the carinal side. In some young specimens, about the tenth of an
inch in diameter, from the West Indies and from New South Wales, the
spur (the position of which I found varied a little in some other
specimens) was placed nearly in the middle of the valve, and very
nearly at right angles to the basal margin; it is possible that these
may be a distinct species, but without larger specimens to judge
from, I think it more probable that this difference in the tergum is
due to variation and youth.
_Structure of Shell and Radii._--The parietal tubes are commonly
elongated in the ray of the circle: the septa are rather thick, and
strongly crenated at their basal edges. The inner lamina of the
walls is strongly ribbed longitudinally. The broad radii have their
sutural edges formed by ridges, with numerous and closely approximate
denticuli: the interspaces between the main ridges are not soon
filled up, and at the bottom, each interspace usually terminates in
a pore or tube; so that the radii are not solid, as in most of the
foregoing species, but porose. The alæ have their edges crenated.
_Basis_, calcareous, of unusual thickness; the inner, or upper
surface, is striated from the centre in rays, corresponding with the
ribs on the inner lamina of the walls. This striated or furrowed
structure in the basis, shows a tendency to its becoming tubular or
porose, as may be inferred from analogous cases in Balanus.
_Animal's body_ unknown.
_Affinities._--This species is rather more closely allied to the last
than to any other. There is a close analogy in the peculiar manner
in which the scuta and terga are articulated together in the two
species: in this species it is effected by the great development of
the articular ridge of the tergum, and in _T. cœrulescens_ by that
of the scutum. The internally striated calcareous basis, and the
internal tubular interspaces between the denticulated ridges of the
radii, are peculiar characters. The white colour, the narrowly and
closely ribbed parietes, and the broad radii, give this species an
aspect, by which it can be easily recognised.