The animal of the _Bulla_ is singular, from possessing-within its
stomach three pieces of a substance resembling bone; these give that
organ the power of crushing or grinding the food, forming a kind
of gizzard. The bony portion of this stomach is represented in the
foreground in the engraving. The Bulla lignaria is about two inches
and a half in length, and is found in the European seas; Lamarck
mentions as many as eleven species.
[Illustration: _Bulla lignaria._]