ill less phosphate of lime in their shells, than has a
lobster compared with a squilla.

Within the capitulum is the sack, which, together with the upper
internal part of the peduncle, encloses the animal's body. The sack is
lined by a most delicate membrane of chitine, under which there is a
double layer of corium; this double layer is united together by short,
strong, transverse bundles of fibres, branched at both ends:[14] in some
genera, the ovarian tubes extend between these two layers. We have seen,
under the head of the Metamorphoses, that the delicate tunic lining the
sack is simply a duplicature of the thick membrane and valves forming
the capitulum, the whole being the posterior portion of the carapace of
the larva slightly modified.

[14] I am much indebted to Mr. Inman of Liverpool for having
kindly sent me excellent specimens illustrating this structure.

_Peduncle._--Its length varies greatly in different species, and even in
the same species, according to the situation occupied by the individual;
its lower end is sometimes pointed, but generally only a little narrower
than the upper end. In outline, the peduncle is usually flattened, but
sometimes quite cylindrical. It is composed of very strong, generally
thick, transparent membrane, rarely coloured reddish, and often
penetrated by numerous tubuli. The underlying corium is sometimes
coloured in longitudinal bands. At each period of growth a new and
larger integument is formed under the old one, which gradually
disintegrates and disappears; the extreme lower point is often deserted
by the corium, and ceases to grow, whilst the whole upper part still
continues increasing in diameter: in length the chief addition is made
(as is clearly seen in those genera having calcified scales), round the
upper margin, at the base of the capitulum. The surface of the membrane
is either naked or superficially clothed with minute, pointed,
articulated spines, or it is penetrated by calcified scales or styles,
(in Ibla alone formed of chitine,) which pass through it to the corium,
and are added to at their bases, like the valves, at each period of
growth. In Lithotrya alone the scales of the peduncle are moulted
together with the connecting membrane. These scales on the peduncle are
generally placed symmetrically in whorls, with each scale corresponding
with the junctions of two scales, both above and below. Except in
_Scalpellum ornatum_ and the fossil _Loricula