Pvn H,i I'UitlS

MODIOLARIA. .
123
is obliquely and finely crenulated : hinge reflected and deeply
indented : inside nacreous and iridescent, notched all round
the edge, except on the ventral side : muscular scars slight and
scarcely perceptible. L. 075. B. 0*45.
Habitat : Imbedded in the skin or outer integument
of Ascidia mentula and other simple Tunicata, or
attached by its byssus to old shells, in the Laminarian
and Coralline zones on all our coasts. It is by no
means rare ;
and sometimes a score of specimens may
be extracted from a large Ascidia. In a fossil state it
The limits of its
occurs in the Red and Coralline Crag.
foreign distribution comprise the sea- bed lying between
Finmark and the iEgean, and reach westward to the
Canaries. On the Norwegian coast Asbjornsen has
given 10, and Danielssen 150 fathoms as its bathymetrical
range. It has not been quoted in any list of
Icelandic, or of North American shells.
On being dislodged from its usual place of abode,
M. marmorata puts out its foot and feels its way in
search of another retreat ; and when it has found one to
its liking, it immediately spins a byssus and securely
fastens itself, sometimes on or within the fold of a
seaweed, or in the crevice of a stone. I have seen it (as
if acting on a sudden impulse, or disliking to be watched)
detach itself from its mooring and set out again on its
The
travels to select a more sheltered or suitable spot.
genesis or development of the animal has been fully and
most ably elucidated by Loven.
This species used to be called the Mytilus discors of
Linne; and it is not improbable that in his description
he included it with the Mytilus discrepans of Mon-
tagu, which we now refer to Linnets species.
epithet " fusca "i in the '
applicable to the present species;
But the
Systema Naturse * is scarcely
and as one of the
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