Pvn H,i I'UitlS

52 PECTINID/E.
pitted, and sometimes very finely and closely striate lengthwise
: muscular scars slight. L. 1*65. B. 1-45.
Habitat :
Every rocky
coast from Shetland to Corn-
wall, often on oyster-beds, and attached, in the adult
state by the whole or last-formed part of its lower valve
to the inside of old bivalve shells, or to rocks, Eschara
foliacea, and other substances. The depth
of water in
which it lives varies from 5 to 85 fathoms, and the
young are occasionally found at low-water mark on
some shores where the tide retires for two or three
fathoms. In a fossil state P. pusio occurs in the Clyde
beds, as well as in the Red and Coralline Crag. Its
extra-British range is considerable, extending from Nor-
way to the Azores on the one side and to the iEgean on
the other.
In more northern seas this species soon fixes itself
permanently to various bodies by means of an agglutinating
secretion ; but in the Mediterranean and more
southern latitudes it usually remains free, or attached
by a byssus only, from which it has the power of
withdrawing or disengaging itself at pleasure. In the
former or fixed state it belongs to the genus Hinnites
of Defrance. It has been clearly shown, however, by
the late Mr. G. B. Sowerby thirty-five years ago, on con-
chological grounds, and by Dr. Fischer in 1862, physiologically,
that this species is a true Pecten, and that the
genus Hinnites is not maintainable. The peculiar mode
of attachment by the shell in this case is the reverse of
that adopted by the oyster, the former having the
smaller valve and the latter the larger valve uppermost.
The prickly scales are sometimes produced also on the
lower valve, and become leaf-like or foliated as in the
oyster. In fixed specimens the byssal sinus is more
or less closed; but I have some of a large size and