decapitated butterfly, brick-red in colour, with an overshirt of fine and
elaborate network, orange tinted. The interior is scarcely less
attractive, the nacre having a pink and bluish lustre, while the "lip" is
dark red. This is found (in my experience) only in association with a
certain species of coral (GORGONIA), which flourishes in strong currents
on a stony bottom three or four fathoms deep. Apart from the unusual
shape and pleasing colours of the shell, it is remarkable because
it seems to be actually incorporated with its host. The foot of the
mollusc is extended into a peduncle, consisting of fibres and tendons, by
which the animal is a fixture to a spur of coral. At the point of union
(to facilitate which there is a hiatus in the margins of the peduncle)
the sarcode or "flesh" of the coral is denuded, its place being
occupied by ligaments, which by minute ramifications adhere so intimately
to the coral stock or stem that severance therefrom cannot be effected
without loss of life to the mollusc.

On a single spray of ruddy Gorgonia several of these commensal molluscs
may occur in various stages of development--the smaller no bigger than the
wing of a fly and almost as frail, the larger three and four inches long,
and each whatsoever its proportions securely budded on and growing from a
spur, while frequently the valves of the large are bossed with limpets
and other encumbrances. In appearance the shell represents a deformity in
usurpation of a thin pencilate "growth" of coral a foot long, for the
exterior colouration is that of the coral. Quite independent of their
host for existence, these molluscs are not to be stigmatised as
parasites, though the individual spur to which each is attached is
invariably destroyed by the union, merely sufficient remaining for the
support of the intruder. Natural science provides many illustrations of
symbiosis, or the intimate association of two distinct organisms. This
example may be out of the common, and therefore worthy of inclusion in a