comparing this lower part of
the carina in _L. australis_ (fig. 5 _a_), with the same part in some of
the species of the allied genus Paecilasma, it would appear that the fork
is formed by an oblong disc, more and more notched at the end, and with
the rim between the two points more or less folded backwards:
conformably with this view, in very young specimens of _L. australis_,
instead of a large and sharp fork, there is a small disc. The only use
of the fork appears to be to give firm attachment to the membrane
uniting the valves and peduncle. In _L. fascicularis_, instead of a
fork, there is a broad, oblong disc (figs. 6, 6 _a_), rectangularly
inflected; it is much longer than the fork, in proportion to the upper
part of the carina; the disc is not more deeply embedded than the upper
part. The umbo (and primordial valve when distinguishable,) of the
carina is seated just above the embedded fork (or disc in _L.
fascicularis_), at the point where the inflection takes place; hence the
main growth of the carina is upwards,--the fork, however, being of
course, likewise added to at its point: in _L. fascicularis_, the growth
is both upwards and downwards.

_Peduncle and Attachment._--The peduncle is generally quite smooth:
though with a high power its surface may be seen to be studded with
minute beads, or larger discs, of yellowish and hard chitine; in the
young of _L. australis_, and I suspect of some other species, it is
covered with very minute spines. The peduncle in this genus attains its
greatest development. The cement-tissue debouches, I believe, only
through the functionless larval antennae, except in one species, _L.
fascicularis_, in which a ball of this substance is formed in a most
peculiar manner round the peduncle (Pl. I, fig. 6), apparently for the
purpose of serving as a float, as will be presently described.

_Size and Colour._--The species of this genus are the largest of the
Pedunculata, with the exception of some Pollicipes: even in the smallest
species (_L. pectinata_), the capitulum sometimes attains a length of
about half an inch. The peduncle varies much in length in the same
species: in _L. anatifera_, it is occasionally above a foot long. The
colours of _L. anatifera_, _L. Hillii_, and _L. anserifera_, are very
bright and striking; the membrane bordering the valves and that round
the top of peduncle in two of the species, is of the brightest
scarlet-orange; the valves, owing to the underlying c