rim
following the curve of the shell about an inch to an inch and a half
within the jagged edge of the epidermis, as shown in the Manilla shell
illustrated herewith, in which the lip, usually trimmed off for
commercial purposes, is preserved. The lining of the meleagrina is not
as iridescent as that of the thin shell varieties.
Thus
the shell is being constantly enlarged at the edge, by a deposit of the
exudations of the mantle; conchiolin for the epidermis outside, lime
for the prisms and inner layers of transparent plates, until the shell
has attained its full growth in size, after which some varieties
continue to lay on nacre only.
The
linings of some have a black rim, extending from the hinge on one
side, around the edge to the hinge on the other side. Viewed from the
edge this dark band appears to be a sixteenth to half an inch wide
(widest at the lip), fading out as it becomes lost under the thicker
white nacre of the interior, but turn the shell up and look at it
squarely from the front and it is black only around the extreme edge
where it joins the epidermis. This kind of shell is found in
the Pacific about the islands of Polynesia and is
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