Pvn H,i I'UitlS

serted they are strongly wrinkled ;
SCROBICULARIA. 439
orifices plain :
triangular, symmetrical, hanging obliquely : palps
gills small,
of the same
size and shape as the gills, smooth outside and pectinated
within :
foot proportionally large, muscular, slightly angulated
at the heel and granular at the point.
Shell oval, rather convex, somewhat inequilateral, thin,
opaque, polished :
nute concentric striae, crossed in some specimens (particularly
towards the beaks) by fine longitudinal lines, which apparently
pervade the whole fabric, as they are equally visible
on the inside surface ; the concentric striae occasionally di-
sculpture, numerous slight, irregular, and mi-
lines of
verge obliquely near the margin, as in S. prismatica ;
growth distinctly marked : colour snow-white, with an opaline
hue : epidermis fibrous, pale yellowish-white : margins more
or less curved in front, rounded on the anterior side, bluntly
pointed on the posterior side, which is sometimes flexuous
and slightly angulated anterior ; dorsal margin gently sloping ;
from the beak at the same
posterior dorsal margin inclining
angle, and expanding outwards where it meets the posterior
margin, so as to form a wedge-like edge ; the terminal angle
on that side is in a line with the transverse axis of the
shell: beaks blunt and incurved; umbones projecting: ligament
short, prominent, reddish-brown or horncolour :
cartilage
curved, dark reddish-brown, constructed and placed like that
of S. prismatica : hinge-line obtusely angular : hinge-plate
thick and strong, occupying about one-fourth of the circumfer-
ence : teeth, in the right valve two minute erect cardinals on the
anterior side of the beak, besides a triangular lateral on each
side, the anterior one being double ; the left valve has only a
single small erect cardinal and a slight posterior
lateral : in-
side nacreous and iridescent, finely and closely striated lengthwise
and microscopically fretted ; margin indistinctly crenu-
lated : pallial scar having a short sinus of the same shape as
the shell, occasionally double in consequence of a shifting of
the base of the tubular fold : muscular scars usually shallow,
anterior triangular and elongated, posterior nearly circular.
L. 0-5. B. 0-8.
Var. 1. radiata. Shell of a thinner texture ; posterior side
marked with one or two clear rays. Syndosmya radiata,
Love'n, Ind. Moll. Scand. p. 44.
Var. 2. curta. Shell contracted at each end and conse-
quently more convex, rather solid; posterior side obliquely
truncate and distinctly angulated.