Pvn H,i I'UitlS

142 ARCID.E.
are crossed by finer longitudinal striae or ribs, giving
the sur-
face a cancellated appearance ; these markings are coarser and
more irregular at the sides, but they do not extend to the
lunule or space below the beaks : colour flake- white under the
epidermis, which is thickish, olive-green, and microscopically
striate like hair- cloth in a transverse direction : margins an-
gular and slightly truncate on the anterior side, curved in
front, and expanding on the posterior side to a wedge-shaped
but rounded : angle beaks rather prominent and blunt, slightly
recurved : lunule furrowed obliquely by strong and irregular
wrinkles (being a continuation of the transverse striae), and
indented or grooved in the direction of the beaks ; it is separated
from the rest of the shell by a ledge, and projects in the
middle so as to form a distinct keel : ligament narrow but
strong : cartilage small, pear-shaped,
contained in a narrow
cavity underneath the beaks and projecting inwards : hingeline
gently curved : hinge-plate broad and strong, occupying
the whole of the dorsal space and rather more than one -third
of the circumference of the shell : teeth sharply pointed, 10-12
on the anterior side and 20-24 on the posterior side of the
cartilage -pit, arranged in nearly straight rows, which diverge
outwards at almost a right angle ; they become larger as they
recede from the beak, in consequence of the progress of
growth: inside cream- colour and slightly iridescent, faintly
striated, or marked with lines which radiate from the beak and
terminate in distinct notches or crenulations on the anterior
angle and in front ; but these notches do not extend to the
posterior angle : muscular scars oval and conspicuous. L. 0'65.
B. 0-7.
Habitat :
Sandy
mud and clay on the west coast of
Scotland, at various depths, as well as in Dublin Bay
(Branscombe and Warren) ; Bantry Bay (Humphreys) ;
and south-west coast of Ireland (M f
Andrew). Captain
Bedford has dredged it in a semifossil state at Lismore,
imbedded in a concrete of indurated clay. It is a local
species.
Loven, Asbjornsen,
and Malm have recorded
it from several parts of the Scandinavian coasts, the
second of these authors giving 15-20, and the last 14-35
fathoms. It also inhabits the coasts of Spain and both
sides of the Mediterranean, as well as the iEgean, where