_Shell white; parietes with the internal lamina generally strongly
ribbed longitudinally, with the pores imperfect and small, sometimes in
part absent; radii narrow, with their summits rounded. Scutum with an
adductor ridge; tergum with the spur truncated and rounded._
_Habitat._--California, Mus. Cuming, Aug. Gould; attached to shells
and wood, together with _B. nubilus_. Southern Pacific ocean,
attached to _Pollicipes polymerus_; Mus. Brit.
_General Appearance._--Shell steeply conical, or cylindrical and
elongated; dirty white; walls rugged, longitudinally folded; radii
narrow, with their summits very oblique and rounded; orifice toothed.
Basal diameter of largest specimen half an inch.
_Scutum_, resembling externally that of _B. crenatus_; rather broad,
surface smooth; articular ridge very prominent, and articular furrow
very wide; hence, when the summits of the opercular valves are worn
down, the two scuta together form a square projection indenting
the two terga, as in _B. balanoides_. Internally, there is a small
adductor ridge, on the lower side of which there is a pit, as if
for a muscle. The depression for the lateral depressor muscle is
small, but variable. _Tergum_ without any longitudinal furrow, and
hardly a depression: spur broad, with its lower end truncated and
rounded; internally, articular ridge very prominent; crests for the
depressores well developed.
_Compartments_:--The internal surface of the parietes is smooth in
the upper part beneath the sheath, but generally very strongly ribbed
in the lower part, the ribs being plainly denticulated at their
bases; in other specimens, the ribs are very small, and even in parts
quite obsolete. The parietal pores are short and imperfect, sometimes
reduced to an extremely minute size, to be detected only when the
walls are broken across near the basal edge, and most carefully
examined; occasionally not even a trace of a pore exists. Hence in
this respect, this species offers a singular case of variation. The
_radii_ are narrow, and of nearly the same width from top to bottom;
their very oblique summits, when well preserved, are smooth and
rounded; their sutural edges are ribbed or crenated with extremely
fine, smooth septa; the recipient furrow is plainly marked by these
septa. The sutural edges of the alæ are crenated; their summits are
less oblique than those of the radii.
_Basis_, thin, finely furrowed in lines radiating from the centre;
margin sometimes deeply sinuous.
_Mouth_: labrum with the central notch rather widely open, with four
teeth on each side of it: palpi with very short spines along their
inner margins: mandibles with the fourth and fifth teeth forming
mere knobs: maxillæ small, with a mere trace of a notch under the
two great upper spines. _Cirri_; first pair with the rami unequal by
three or four segments, the longer ramus being only one quarter of
its own length longer than the other ramus. Second pair short, with
the segments (and those of the shorter ramus of first pair) somewhat
protuberant. Third pair with the rami one third longer than those of
the second pair. Sixth pair with the upper segments elongated, and
bearing six or seven pairs of spines.
_Affinities._--This species in general appearance closely approaches
_B. crenatus_ and _balanoides_, and it is related to them in many
essential parts, such as in the opercular valves. It agrees with _B.
balanoides_, and differs from _B. crenatus_, in the smallness and
imperfection of the parietal pores, and in the radii having rounded
summits; it agrees with _B. crenatus_ in the structure of its basis,
and in the prominent longitudinal ribs on the internal surface of the
parietes, and differs from that species in the spur of the tergum
being squarer, and in the scutum having an adductor ridge.
_Range._--From the appearance of the Californian specimens, I suspect
that they had adhered to tidal shells and to wood. The specimens in
the British Museum, adhering to _Pollicipes polymerus_, consist of
two lots, one of unknown origin, and the other certainly brought from
the southern half of the Pacific Ocean by Sir James Ross: it deserves
notice, that the _Pollicipes polymerus_, the supporting object,
ranges from California to the southern Pacific Ocean.
_Section_ E.
_Basis membranous._