_Parietes and base porose: shell white, or faintly tinged with purple.
Scutum with the basal margin protuberant in the middle. Tergum with
the longitudinal furrow closed in the upper part: spur not closely
adjoining the basi-scutal angle._
_Hab._--Attached to Milleporæ, Singapore, Mus. Cuming. West
Indies,[89] Mus. Brit.--Mus. Stutchbury.
[89] This specimen in the British Museum was purchased at the sale
of the Rev. L. Guilding's collection, and therefore it is not
certain that this habitat is correct; but as it was sold in the
same lot with a Cirripede certainly West Indian, and as the main
collection was made in the West Indies, this habitat may, I think,
be trusted.
I have considerable doubts whether it would not have been more correct
to have placed this species in the last section, instead of where
it now stands; it certainly is more closely allied to _B. Ajax_,
especially in its operculum, than to the following species; yet the
fact of the radii not being permeated by pores does not permit of its
admission into the last section; and both in habits and structure it
undoubtedly comes very near to the following species. Those varieties
which are not much elongated, and which have the basis nearly flat,
would certainly, if considered by themselves alone, not have gained
admission into our present section.
_General Appearance._--Shell conical, somewhat globular, more or less
elongated in the rostro-carinal axis, owing to the basal production
of the rostrum. Orifice, rather small, entire, oval, pointed at the
carinal end. Radii moderately broad, with their summits parallel to
the basis. Colour dirty white, often faintly tinged with purple;
sheath, pale purplish-blue. Surface extremely smooth; the parietes
are generally covered (as viewed through a lens) by a very thin,
yellowish epidermis, giving to the whole a glistening, granular
aspect: the radii are generally destitute of this epidermis, and are
therefore of a dead white. The basis is concave, and sometimes deeply
cup-formed; it is, however, not symmetrical; sometimes it is flat.
Basal diameter of largest specimen, including the basis itself, 1.5
of an inch in the longitudinal axis; transverse diameter, 1 inch; the
inequality in the length of the two diameters is rarely so great as
in this unusually large specimen.
_Scuta_, externally very convex, with the growth-ridges extremely
prominent; basal margin sinuous, the middle portion being prominent;
this is best seen in young specimens (Pl. 3, fig. 2 _d_). Internally,
the articular ridge is broad and reflexed. The adductor ridge in the
upper part is almost confluent with the articular ridge; it runs down
to the most prominent point of the basal margin; in young specimens
it is sharp and prominent; in old specimens it is very blunt and
little prominent. There is a rather deep hollow for the lateral
depressor muscle. In young specimens there is a small, depending,
blunt tooth at the basi-tergal angle, which helps to make the basal
margin more deeply sinuous.
_Terga_, with the longitudinal furrow closed, except on the spur
itself, where it is open. The spur is moderately long and broad, but
varies in breadth; it is placed at rather less than its own width
from the basi-scutal angle; its lower end is obliquely rounded; the
basal margin on the opposite sides of the spur, together form a
nearly straight line. The whole valve is rather broad. The crests for
the tergal depressores are barely developed.
The _Compartments_ have rather large parietal tubes; the septa are
coarsely denticulated at their bases; the internal lamina is smooth,
except close to the basis. The _radii_ have their summits parallel
to the basis; their sutural edges are formed of rather thick septa,
which stand at an unusual distance apart from each other, and have
perfectly symmetrical, minute denticuli on each side. The interspaces
between the septa are filled up solidly to within a short distance of
the surface; but yet not so completely as in the following species,
and as in those in the succeeding sections of the genus; this is what
might have been expected from the close affinity of _B. stultus_ to
_B. Ajax_, in which latter the radii are still permeated by pores,
though smaller than is general in the species of our first section
(A). The _alæ_ have their summits extremely oblique, and their
sutural edges, I believe, smooth. _Basis_ porose, with an underlying,
finely-cancellated layer.
_Mouth_: labrum with six small teeth; mandibles with the 3d tooth
blunt; the 4th minute, and the 5th almost confluent with the inferior
angle. Maxillæ with the edge straight and simple. _Cirri_ partly
destroyed; on each segment of the sixth pair there were five pairs of
spines.