_Shell, when well preserved, violet-purple: sutures, when not
obliterated, formed by oblique interfolding laminæ: basis membranous,
but surrounded by a ledge formed by the inflected basal edges of the
parietes: scutum and tergum completely calcified together._
_Hab._--Philippine Archipelago; Mus. Cuming.
_General Appearance and Structure._--Shell depressed, with a
large diamond-shaped orifice. Colour beautiful violet-purple, but
externally much obscured by disintegration, causing the shell to
be ashy gray. Walls smooth or slightly folded. Sutures generally
quite, or almost quite obliterated; but when well preserved, they
differ remarkably in appearance from those in the foregoing species;
for the radii externally here consist of oblique plates or laminæ
arising on both sides of the sutures, standing nearly parallel to the
parietes, and interfolding with each other. These laminæ are rather
plainly marked by lines of growth. Essentially the radii do not
differ much from those in _C. dentatus_ and _Hembeli_; we have but
to produce obliquely upwards the transverse and interlocking ribs on
their radii, and so convert them into laminæ. During the diametric
growth of the shell, the sutural edges of the alæ are added to, in
the usual manner, by upturned lines of growth; and, in addition, the
recipient furrows of the alæ are similarly added to, so that the
lines of growth are upturned, and alæ appear to have been developed
on both sides of the sutures in the same way as the radii appear to
have been developed on both sides in many Chthamalinæ, though rarely
in the Balaninæ. The inside of the shell is beautifully coloured rich
violet; it is punctured with small holes as so often is the case with
_C. stellatus_. In every specimen (all full-grown) which I opened,
the inner basal edges of the parietes were inflected rectangularly
inwards, forming a smooth-edged ledge all round the basal membrane,
which, in proportion to the width of this ledge, was by so much
reduced in diameter. The largest specimen which I have seen was .35
of an inch in basal diameter.
_Opercular valves._--The scuta and terga, in all the specimens which
I have seen, were firmly calcified together; in some, a trace of a
suture could be seen externally, but hardly a trace internally. In
one specimen, there were vestiges of some impressed lines on the
scutum, in exactly the same position in which such occur in _C.
Hembeli_. The scutum is rather narrow. The basal margin of the tergum
is either straight, or depends a little on the scutal side, thus
producing a small spur: the crests for the depressor muscles are
strongly marked, and depend beneath the basal margin.
_Mouth._--The labrum is strongly toothed: the palpi have long hairs
along the exterior basal margin: the mandibles have only three main
teeth, and the inferior coarsely pectinated portion is short; the
maxillæ deeply notched. _Cirri_: the first and second pairs have
their rami slightly unequal in length; the third pair differs from
the same pair in the other species of the genus, in having some few
of the basal segments on the anterior ramus thickly clothed with
spines, so as to be brush-like: there is even a trace of a similar
structure in the lowest segments of the posterior ramus. In the three
posterior pairs of cirri the segments are much elongated, and support
four pairs of spines.
_Branchiæ._--Unknown.