Pvn H,i I'UitlS

MACTRA. 423
white variegated by longitudinal rays of light reddish-brown,
which are often confluent, or arranged in sets ; purplish at the
beaks ; lines of growth represented by white bands or zones :
epidermis yellowish-brown, laminar, and glistening, at the posterior
end fibrous and frequently ramified or interlacing, so
as to resemble some of the sessile kinds of Tubulariidce :
margins regularly curved in front, and obtusely angular at
both ends, with a slightly rounded slope or deflexion on each
of the dorsal sides from the beak to the terminal angles ; the
anterior and posterior sides are somewhat angulated, the latter
more distinctly : beetles sharp, triangular, and incurved, turned
a little towards the anterior side ;
umbones swollen and pro-
minent, but not much projecting : ligament short and slight,
yellowish-brown: cartilage triangular, compact, reddish-brown
or chestnut, placed obliquely as in the other species : hinge-
line curved : lunge-plate very broad, strong,
and flexuous in
consequence of the projection of the cartilage-pit and adjacent
part : teeth, in the right valve a short, laminar, and erect car-
dinal, nearly parallel with the hinge-line, and another of the
same description and height, placed at a right angle to the
first, and forming one of the side-walls of the cartilage-pit ;
both these lie directlv under the beak and on the anterior side :
laterals two on each side, thin, erect, laminar, elongated, quite
smooth and polished ; the outer are shorter and smaller than
the inner pair; in the left valve are two erect and laminar
cardinals of equal size and height, united throughout at the
back and diverging at a right angle, like the flaps of a single
this valve has also a thin, erect, laminar and
folding screen ;
elongated lateral on each side, which are higher in the middle
and curve gradually to their bases : inside white, marked with
clear specks, and minutely freckled, .slightly
striated in a lon-
gitudinal direction: pallial scar distinct, with a very short
sinus representing an arc of three-fourths of a circle : muscular
scars also distinct, irregularly oval and nearly equal-sized.
L. 1-5. B. 2.
Var. cinerea. Shell rather more solid, ashy-grey or creamcolour,
without rays. M. cinerea, Montagu, Test. Brit. Suppl.
p. 35.
Habitat :
From
the verge of low-water mark at
spring- tides to 18 fathoms (Goodwick Bay, Pembroke-
shire), in sandy tracts; and the variety also is widely
distributed. This species occurs, but not commonly,