_Parietes and basis not porose: carino-lateral compartments very
narrow, and of nearly the same width from top to bottom: radii with
their sutural edges smooth. Scutum externally striated longitudinally._
_Hab._--Attached to Gorgoniæ, Tubicoreen, Madras (associated with _B.
calceolus_), Dr. Johnston. Hab. unknown, Mus. Brit. and Darwin.
This is a very distinct form, though nearer to the foregoing than to
the other species. Its separation from the sub-genus Acasta is quite
artificial; its affinity to this sub-genus is shown by its weaker
shell, non-porose parietes and basis; by the radii having their sutural
edges smooth, and their summits not quite square; by the carino-lateral
compartments being very narrow; by the less elongated basis, not
furrowed, from not clasping the branches of the Gorgonia; and by the
longitudinally striated scuta; nevertheless, from the similar habits,
and from the graduated structure in the five foregoing species, it
cannot be removed out of the genus Balanus. I have seen three sets of
specimens of this species.
_General Appearance._--Shell, sometimes with the rostrum, and
sometimes with the carina, and corresponding portions of the basal
cup, elongated; but not, apparently, to so great a degree as in
the foregoing species; basis not furrowed, from not clasping the
branches of the Gorgonia. Colour pale blueish-purple, with the
radii whiter. The surface is studded with small calcareous points.
The carino-lateral compartments are very narrow, not more than one
tenth of the width of the lateral compartments; they are, moreover,
scarcely wider at the base than at the summit. The summits of the
radii are, apparently, a little oblique, or at least not so square as
in the foregoing species. The shell is not nearly so strong as in the
last three species; and the compartments separate by gentle force,
and from the action of caustic potash. The largest specimen was .4 of
an inch in basal diameter.
Internally, the parietes are not very strongly ribbed, or they are
almost smooth, and there are no pores. The basis is concave and
smooth within, and is not porose. The sutural edges of the radii are
quite smooth, or sometimes they exhibit, in the lower part, mere
traces of septa,--a character by itself sufficient to separate this
from the foregoing species. The alæ have oblique summits, and the
rather narrow portion added during the diametric growth of the shell,
is white.
The _Scutum_, externally (6 _d_), has raised striæ, radiating from
the apex; valve rather thick; internally, the articular ridge is but
slightly prominent, and its lower end is rounded off: the depression
for the lateral depressor muscle is slight; between this depression
and that for the adductor muscle, the surface of the valve is
prominent. _Tergum_, somewhat beaked; externally, the surface is
depressed in the line of the spur: the carino-basal margin slopes
towards the spur.
_Animal's body_ unknown.
_Section_ C.
_Parietes and basis permeated by pores. Radii not permeated by pores._