_Parietes ribbed, mottled purplish-red; orifice broad, trigonal, hardly
toothed. Scutum thick, with from one to six longitudinal rows of little
pits. Tergum without a longitudinal furrow; spur truncated, fully one
third of width of valve._
_Hab._--Java; East-Indian Archipelago; Peru; West Columbia;
California; Sydney; New Zealand. Mus. Brit., Cuming, Stutchbury,
Dunker, &c.
_General Appearance._--Shell conical, generally depressed; orifice
broad, triangular, almost equilateral; walls coloured or only mottled
with purplish-pink, having either irregularly branching, or regular,
longitudinal ribs, which are generally white. The radii are pale
pink, or nearly white: the opercular valves have either their upper
parts, or nearly their whole surface, clouded with pinkish-purple:
the epidermis is not persistent: the walls are moderately strong: the
largest specimen was one inch, but generally full-grown specimens are
about half an inch in basal diameter.
The _Scuta_ have the lines of growth highly prominent. From one to
five or six rows (7 _b_, 7 _c_) of nearly circular, or transversely
oblong, deep pits, extend down the middle of the valve; rarely there
is not even one row; in this latter case, the valve is not striated
longitudinally. These little pits are caused by one or more deep
longitudinal furrows, crossed by the lines, or rather ridges, of
growth. In the same group of specimens, I have seen individuals with
three, five, and six rows; and even a few specimens with only one
row, or none at all. The outline of the valve is elongated, with the
apex slightly reflexed: the inner surface is protuberant, sometimes
to a remarkable, but variable degree. The articular ridge is not
very prominent, but it extends fully half-way down the valve, and
generally ends in a small free point. There is a short adductor
ridge, and a deep narrow pit or cleft for the lateral-depressor
muscle. _Terga_, externally smooth, flat, with scarcely a trace of
a longitudinal furrow; spur broad (7 _e_, 7 _f_), varying from half
to one third of the width of the valve, with the end truncated,
situated either near or quite close to the basi-scutal angle. The
crests for the depressor muscles are moderately well developed.
_Compartments._--The parietal tubes are, in their upper parts, filled
up solidly, without transverse septa. The radii generally have their
summits slightly oblique, and this is almost always the case with the
radii of the rostrum; the other radii sometimes extend from tip to
tip of the parietes, and are parallel to the basis; rarely the radii
are considerably oblique. The septa of the radii are very obscurely
denticulated, and the interspaces between them are filled up solidly.
The alæ have their sutural edges thin and smooth.
_Mouth._--Labrum with three teeth close together on each side of the
central notch: mandibles with four teeth, the fourth being small, the
fifth either absent or scarcely distinguishable from the inferior
angle: maxillæ without any notch, with the two lower spines rather
longer than the others. _Cirri_: In the first pair, one ramus is only
half the length of the other; in the second pair, both rami are short
and about equal in length; in the posterior pairs, the segments,
which are not protuberant, bear four pairs of spines, of which the
three lower pairs are short.
This species is widely-distributed, and where found seems to be common.
It is generally attached to shells of mollusca, but I have seen it also
attached to wood. I have found it associated with _B. tintinnabulum,
var. concinnus_, and _coccopoma_, with _B. psittacus_, _improvisus_ and
_amphitrite_, and with _Elminius modestus_.
Young specimens bear a considerable resemblance to certain young
varieties of _B. tintinnabulum_, and can indeed be distinguished
from them only by a careful examination of the opercular valves; for
it should be borne in mind, that in certain cases the scuta in _B.
tintinnabulum_ are pitted with little cavities. This species in some
respects is, I think, allied to _B. porcatus_, but it is far more
closely related to _B. spongicola_, and can be discriminated with
difficulty from certain varieties of this latter species. In Mr.
Cuming's collection, there is a group of small specimens, crowded
between some older specimens, which are remarkable from the shell being
oval in a transverse section,--from the smoothness of the walls,--and
from the absence of pits on the scuta; yet there could be no doubt that
these specimens belonged to our present species.