e manner as the valves; each is furnished with one or more
tubuli, in connection with the underlying corium. In _P. sertus_ and _P.
spinosus_, the scales are small, spindle-shaped, and not of equal sizes,
and the rows are distant from each other, so that their alternate
arrangement is not distinguishable; in these two species, new scales are
formed round the summit of the peduncle, and the growth of each is
completed whilst remaining in the uppermost row; but, besides these
normal scales, such as exist in the other species of Pollicipes and in
Scalpellum, new scales are formed in the lower part of the peduncle,
which are generally of very irregular shapes, are often larger than the
upper ones, are crowded together, and sometimes do not reach the outer
surface of the membrane. This formation of scales in the lower part of
the peduncle, independently of the regular rows round the uppermost
part, is perhaps a feeble representation of the calcareous cup at the
bottom of the peduncle in the genus Lithotrya. The prehensile antennae
will be described under _P. cornucopia_.

_Size._--Most of the species are large: and _P. mitella_ is the most
massive of the Pedunculated Cirripedes.

The _Mouth_ is not placed far from the adductor muscle. The labrum is
highly bullate. The mandibles have either three or four main teeth (Pl.
X, fig. 1), with often either one or two smaller teeth inserted between
the first and second. The maxillae (Pl. X, figs. 13, 14), have their
edges either straight and square, or notched, or more commonly with two
or three prominences bearing tufts of finer spines. The outer maxillae
(fig. 17) generally have a deep notch on their inner edges, but this is
not invariable. The olfactory orifices in most of the species are highly
prominent.

_Cirri._--The first pair is never placed far distant from the second.
The posterior cirri have strong, somewhat protuberant segments; and
between each of the four or five pair of main spines (Pl. X, fig. 27),
there is a rather large tuft of straight, fine, short bristles. The
second and third pair have the basal segments, either of the anterior
rami, or of both rami, so thickly clothed with spines (fig. 25), as to
be brush-like: in _P. mitella_, however, the third pair is like the
three posterior pair in the arrangement of its spines, in this respect
resembling the sessile Chthamalinae. The caudal appendages are either
uni-articulate and spinose, or multi-articulate: it is re