Pvn H,i I'UitlS

ANOMIA.
plates, which are alternately high and low; and the stri-
ated appearance of the top or outer covering is pro-
duced by the edges of the higher plates. This appendage
is capable of receiving a high degree of polish, and m
that state it resembles ivory and is equally close-grained.
In the fry the orifice is larger in proportion to that of
the adult, and is placed on one side. The beak of
young specimens is sometimes much produced, and at
other times slightly incurved. When the shell is thin,
the long muscular scar seen through the upper valve
resembles a white line. The varied and nacreous hues
of the shell rival in lustre those of an opal. A group
of these specimens from Lulworth Cove, on a valve of
Pecten opercularis, now before me,
33
are of different
colours, white, yellow, and pink, and reflect their pearly
gleams in every direction. In substance the shell bears
some affinity to talc. Specimens from Bantry Bay,
Lough Strangford, and Exmouth roads are larger than
usual. One from the first-named localitv measures four
inches in diameter. Now and then, but rarely, the
upper valve is flat, and the lower or perforated valve is
convex ; and in one case the front half of the shell is
divided into two distinct lobes, owing to the continual
obstruction and irritation caused by a small branch of
Sertularia abietina, which had insinuated itself and
grown up
in front of the Anomia. But a more curious
instance of an adaptation to circumstances is presented
by specimens which I found many years ago on a mussel-bed
in Swansea Bay, laid bare by an unusually low
tide. The orifice in every specimen was completely
closed by a series of thin vaulted plates of the same
material as the shell. All the specimens were living,
and attached to the mussels by the byssal threads of the
latter. It appeared to me that, having
been acciden-
c o