There are two others found in shells resembling those of the
testaceans. One of them is nicknamed by some persons the nautilus or
the pontilus, or by others the 'polypus' egg'; and the shell of this
creature is something like a separate valve of a deep scallop-shell.
This polypus lives very often near to the shore, and is apt to be
thrown up high and dry on the beach; under these circumstances it is
found with its shell detached, and dies by and by on dry land. These
polypods are small, and are shaped, as regards the form of their
bodies, like the bolbidia. There is another polypus that is placed
within a shell like a snail; it never comes out of the shell, but
lives inside the shell like the snail, and from time to time protrudes
its feelers.

So much for molluscs.