Pvn H,i I'UitlS

CARDIUM. 295
ceptible by the naked eye : colour yellowish-white, beautifully
mottled in the young and near the beaks of the adult with
blotches or longitudinal streaks of reddish-brown or fleshcolour :
epidermis thin, consisting of a tissue of exceedingly numerous
and delicate fibres, woven in a transverse direction, frequently
anastomosing or becoming blended together, and varying in
colour from yellow to brown : marc/ins curved in front and
at the sides, with a slight tendency to form an angle at the
posterior extremity ; the rounded contour is only interrupted
behind by the prominence of the umbonal area : beaks small,
almost touching each other, slightly recurved towards the
anterior side : tunule indistinct, but having projecting lips :
Ugamentlojig, spindle-shaped, horncolour, and continued under
the beaks on the anterior side : hinge-line obtuse-angled :
hinge-plate broad, reflected fourth of the circumference :
outwards, not occupying one-
teeth, in the right valve two cardinals,
a strong triangular lateral on the anterior side and a
smaller pointed lateral on the posterior side ; in the left valve
are also two cardinals, two laterals (the lower one being very
much larger than the other) on the anterior side and one
short triangular lateral on the posterior side ; the cardinals are
relatively of the same size in each valve : inside porcellanous,
closely and microscopically striated like the epidermis, sometimes
of a chocolate colour, or variegated with reddish-brown ;
margin fluted in the middle and towards the sides, but only
notched near the hinge-line : pallial
scars oval and deep. L. 2-4. B. 2*3.
scar distinct : muscidar
Var. 1. gibba. Shell smaller, having a more oblique con-
tour, and gibbous.
Var. 2. rotunda. Shell flatter and rounder.
Var. 3. pallida.
Habitat :
Shell of a uniform strawcolour.
Generally, but locally, diffused throughout
the British seas, on sandy and nullipore bottoms, in 5-
80 fathoms. Var. 1. Exmouth (Clark); Swansea and
Bantry Bay (J. G. J.); Milford Haven (Jordan). Var. 2.
Birterbny Bay, Connemara (Barlee)
. Var. 3. Exmouth
(Clark); Sark (J. G. J.). This species is a member of
our more recent pliocene beds, as well as of the Coral-
line Crag. Mr. Rose has found a specimen in a stratum