_Shell dirty reddish-purple, steeply conical: radii narrow: basis
obscurely porose. Scutum with the lines of growth crenated: tergum with
the spur truncated, broad as half the valve, and depending beneath the
basi-scutal angle as much as half its own breadth._
_Hab._--Japan, attached to an Isis, Mus. Cuming. Attached to an
oyster, Mus. Stutchbury.
As already stated, this species comes in all essential respects very
near to the last, though differing much in appearance; I have seen
two sets of specimens, and two sets of _B. allium_, and there was no
variability or passage in the points in which they differed; hence I
must consider them as specifically distinct.
_Shell_, steeply conical, strongly but bluntly ribbed longitudinally;
coloured either all over dull reddish purple, or with the upper part
only pinkish purple: in one set of specimens, the yellow epidermis
was partially persistent. Radii narrow. Orifice small, ovate. The
wall of the carino-lateral compartment is very narrow. The internal
surface of the parietes is ribbed, but finely, and only in the lower
part. The septa, on the sutural edges of the radii, are finer than in
_B. allium_. Basis flat, obscurely permeated by pores. The largest
specimen is .25 of an inch in basal diameter.
_Scuta_: these are longitudinally and finely striated; the
basi-tergal corner is more rounded off than in _B. allium_, and the
articular ridge is not nearly so prominent: internally, the adductor
ridge is rather more prominent. The _Tergum_ is rather broader: its
apex is produced into a minute sharp point: the scutal margin is
straight; the spur is broader, and measured from the basi-scutal
angle of the valve, considerably longer; namely, as long as half
the width of the basal margin of the spur, whereas in _B. allium_
it is only about a quarter as long as the basal margin of the spur:
the lower edge of the spur is not here so directly transverse to
the longitudinal axis of the valve as in _B. allium_: the external
surface is not so flat as in that species, and a depression runs down
to the basi-scutal angle of the spur.
Considering the difference in the shape and appearance of the shell,
with its narrow radii and small orifice; considering the less strongly
ribbed internal lamina of the parietes, the finer septa on the sutural
edges of the radii, the slight difference in outline in the scuta and
terga, more especially the greater length of the spur, I conceive I am
right in ranking this form as a distinct species, though assuredly it
is very closely allied to _B. allium_, and even still closer to the
following _B. quadrivittatus_.