hin the cup of
_L. Nicobarica_ I found a lately-formed layer of shell, projecting
1/10th of an inch on one side of the cup, and by its protuberance
distinguishable even through the old coat of the peduncle, which was
nearly ready to be moulted. In an analogous manner, in the capitulum of
_L. dorsalis_ and _L. truncata_, I have found a new peduncular membrane
bearing the usual, but then sharp, calcified scales, attached to the
lower projecting edge of the last-formed shelly layer, lying under the
old peduncular membrane, which was attached to the penultimate layer of
shell, and with its worn scales was just ready to be moulted.

The final cause of the moulting of the calcified scales, together with
the membrane of the peduncle to which they are attached,--a case
confined to Lithotrya,--I have scarcely any doubt is the reproduction of
a succession of scales, sharply serrated for the purpose of enlarging
the cavity in which the animal is lodged. The extreme thinness of the
membrane of the peduncle has been noticed; this may be partly related to
its protected condition, but partly, I think, to the necessity of its
being formed in a very extensible condition; for the new coat, owing to
the projection of the new shelly layers under the valves, and within the
basal cup, is by so much shorter than the old peduncle, yet after
exuviation it has to stretch to a greater length than the old membrane,
to allow of the growth of the Cirripede. Owing to the thinness and
fragility of this membrane, the basal attachment of the Cirripede is, no
doubt, chiefly effected by the unusually strong longitudinal muscles;
and the necessity of a surface of attachment for these muscles, stronger
than the external membrane of the peduncle, probably is one of the final
causes of the basal calcareous disc and cup, and likewise for the
unusual manner in which the valves of the capitulum are locked together
by folds and small roughened projections. The basal discs and cup,
however, apparently serve for several other purposes, namely, for
raising the animal a little in its burrow, (which is narrow and pointed
at the bottom,) at that period of growth when it has ceased to burrow
downwards, but still increases in diameter; also for carrying the
animal, as over a bridge, across any pre-existing cavity in the rock;
and lastly, perhaps, for removing lower down, in the intervals of
exuviation, the point of attachment for the longitudinal peduncular
muscles.

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