_Shell white, strongly ribbed longitudinally, with the basal margin
produced into long points: basis concave, not permeated by pores, but
strongly ribbed externally in radiating lines; the interspaces between
the ribs being riddled by minute rounded apertures, often placed in
double rows._
_Hab._--Unknown, Brit. Mus., attached to a lamelliferous coral.
I have in this instance broken through my rule of not describing a
Cirripede without examining the opercular valves; but the species here
named is so peculiar, that it would have been a fault to have passed it
over. There is but a single specimen in the British Museum, without, as
just stated, the operculum, and of course without the animal's body.
_Shell_, white, depressed, conical, somewhat elongated in its
rostro-carinal axis; orifice rather small, pentagonal, toothed,
elongated. Parietes rather thin, with extremely prominent
longitudinal ribs, produced at the basal edge into long spikes: the
internal surface is also ribbed, but less strongly than the outside.
Radii rather narrow, with oblique, not smooth summits; sutural edges
very finely and obscurely crenated. Alæ with their summits extremely
oblique. Lower edge of sheath closely attached to the walls. The
carino-lateral compartments are rather narrow.
_Basis_, slightly concave or saucer-shaped; the circumference
is produced into long spikes, corresponding with those on the
basal margin of the parietes: these projections equal half the
semi-diameter of the shell. The internal surface of the basis has
slightly prominent, rounded ridges; and the external surface has
extraordinarily prominent, sharp ridges, radiating from the centre;
the edges of the external ridges are irregular, notched, and knobbed.
I have seen in no other species external ridges on the basis or
surface of attachment; and what is more remarkable, the interspaces
between the ridges are penetrated by small rounded apertures, of
irregular shape and unequal sizes; and these are generally arranged
in an irregular double row, and externally are closed by the
membrane, which clothes the basis. In the sub-genus Acasta, the basal
cup is sometimes penetrated by similar holes, but these seem never
to extend over the whole basis, and are very variable; nevertheless,
in some specimens of _Acasta spongites_ from the Cape of Good Hope,
portions of the basis closely resembled, except in the absence of
the radiating ridges, the structure here described, but the holes
were not arranged in any definite order. The internal surface of
the parietes in _Acasta sporillus_ presents a somewhat analogous
appearance, but the pits do not penetrate through the walls. This
species, I have no doubt, is closely allied to the sub-genus Acasta,
and to _Balanus navicula_ with its allies, and, but much less
closely, to _B. allium_ with its allies. Indeed, had _B. terebratus_
inhabited a sponge, I should have been compelled to have ranked it in
the sub-genus Acasta.