mother-of-pearl
oyster shells is the "blister." It is produced by the raising of the
nacreous deposits above the level of the shell to cover some intruder
of considerable size. This results in a growth similar in shape to a
blister on the flesh, hence the name. It is cut out of the shell and
used in various ways as a set for jewelry, or to imitate the bodies of
insects or small animals. Others with a slightly higher dome and
rounded oval shape, regular in form, are called "turtlebacks."
Some
of these hollow shells of pearl have been found to cover small fish,
lizards, etc. The writer saw one which appeared to be a large
button-pearl. On lifting, it proved to be a shell of several
thicknesses of nacre covering a small shell-fish about a half-inch in
diameter. The imprisoned mollusk was shrunken and crumbling so that
the nacreous covering could be lifted from over it, a hollow dome of
pearl. Mud blisters are common in some waters and depreciate the
quality of the shell and are otherwise useless. A typical mud blister
appears in the shell illustrated herewith.
The Abalone pearl occurs usually as a baroque 92
