The following comprehensive notice of the substance is taken from a modern history of a voyage to the South Seas.
"It is that _mollusca_ from the Indian Seas which is known to commerce by the French name _bouche de mer_ (a nice morsel from the sea).

If I am not much mistaken, the celebrated Cuvier calls it _gasteropeda pulmonifera_.

It is abundantly gathered in the coasts of the Pacific islands, and gathered especially for the Chinese market, where it commands a great price, perhaps as much as their much-talked-of edible birds' nests, which are properly made up of the gelatinous matter picked up by a species of swallow from the body of these molluscae.

They have no shell, no legs, nor any prominent part, except an _absorbing_ and an _excretory_, opposite organs; but, by their elastic wings, like caterpillars or worms, they creep in shallow waters, in which, when low, they can be seen by a kind of swallow, the sharp bill of which, inserted in the soft animal, draws a gummy and filamentous substance, which, by drying, can be wrought into the solid walls of their nest.

Hence the name of _gasteropeda pulmonifera_.
"This mollusca is oblong, and of different sizes, from three to eighteen inches in length; and I have seen a few that were not less than two feet long.