Pvn H,i I'UitlS

CARDIUM. 271
semioval ; the upper pair are as long as the lower, but not
half the depth : palps very long, slender and pointed, strongly
striated on the inside and less so on the outside : foot finger-
shaped, closely striated lengthwise,
covered with a flesh-
coloured or vermilion delicate skin, under which it is pure
white ; its length is at least twice that of the shell.
Shell roundish, very convex, rather solid, opaque and
of a dull hue : sculpture, about 20 strong
but somewhat com-
pressed ribs, which are a trifle broader than the furrows be-
tween them ; the crest of each rib has a numerous row of
triangular and short but stout spines,
which are connected
together at the base and are usually curved towards the posterior
side ; all these spines are nearly equal in diameter and
length; both ribs and furrows (especially the latter) are crossed
by nexuous wrinkles, which are coarser and more distinct on
the posterior side; in young specimens are observable some
longitudinal lines and microscopical markings similar to those
noticed in the description of the last species : colour yellowish -
white : epidermis fibrous, mostly obliterated : margins rounded
on the anterior side, and sloping to the front, which is curved,
but much less obliquely than in C. aculeatum ; posterior side
not much produced, although considerably broader than the
other, slightly truncate, and exhibiting a narrow and indistinct
gape : beaks more or less contiguous ; umbones tumid ; below
the beaks on the anterior side is a nearly smooth heart-shaped
space, the lips of which project or pout, especially on the upper
brownish -
part : ligament shaped like that of the last species,
homcolour : hinge-line obtusely curved : hinge-plate reflected,
occupying about one.-third of the circumference : teeth, in each
valve two erect nearly equal-sized cardinals, with laterals
similar to those of the other : species inside and scars the same.
L. 2-2. B. 2-3.
Yar. 1. expansa. Shell rather more depressed and spread
out at each end.
Var. 2. ovata. Shell transversely oval ; ribs sharp, obliquely
radiating, and much narrower than the furrows ; transverse
dorsal
striae fewer than in typical specimens of a similar size ;
margin nearly straight ; there is only a single minute cardinal
tooth in each valve, besides indistinct laterals. L. 0-125.
B. 0-15.
Habitat :
All our sandy coasts, at various depths
from 5 to 100 fathoms. It occurs in almost every