Pvn H,i I'UitlS

ARCA. 181
yellowish, irregularly mottled with reddish-brown : epidermis
light brown, filamentous, and forming rows of short leaf-like
bristles in the interstices of the longitudinal ribs, becoming
thicker towards the front and at the sides : margins
rounded
on the anterior side, which is very short, flexuous in front,
wedge-shaped and pointed at the posterior side, where a sharp
keel runs obliquely from the beak to an acute angle at the
extremity of the posterior slope : byssal sinus long and wide :
beaks small, slightly recurved, and widely separate from each
other owing to the extent of the ligamental area :
ligament
thin, of a golden-brown tint, lozenge-shaped and composed of
several strips or bands placed diagonally; ligamental cavity
very large and deep, usually smooth, but occasionally striated
by the impression of the ligament : hinge-line straight, forming
nearly a right angle at each extremity, its length equalling
the entire breadth of the shell : hinge-plate broad and strong,
considerably wider at the posterior extremity : teeth 40-50,
arched, perpendicularly striated on both sides and having their
crests consequently notched those on the ; posterior side are
of them are double : inside porcellanous,
partly stained with reddish-brown and green blotches ; margin
the longest, and many
slightly crenulated, especially on the anterior side : pallia!
scars flexuous : muscular scars oval, very large and conspicuous.
L. 0-85. B. 1-5.
Habitat :
Rocky, stony, and shelly ground
on all
our coasts and at all depths. In Bantry Bay it is not
uncommon at low water, closely wedged in the chinks
of slate-rocks, the shape being
distorted and the surface
scraped in consequence of the confined position.
The
abrasion is perhaps caused by the uneasiness of the
animal, through
its continual endeavours to extricate
itself or change its place. In deeper water (20-90
fathoms) it occupies the crevices of large stones and the
hinge-cavities of old bivalve shells. In all cases it is
firmly attached by its byssus, and not a slight degree of
force will suffice to dislodge it. It is a Red and Coral-
line Crag fossil. The foreign distribution of this species
extends from Finmark to the iEgean Sea on the east,
and to the Azores and Canaries on the west. Asbjorn-