Pvn H,i I'UitlS

266 cardiid^:,
ments :
gills short ; upper pair smaller than the lower : palps
triangular : foot sickle -shaped.
Shell convex, closed in nearly every case : beaks bent in-
wards, but scarcely (if at all) to one side : teeth, in the right
valve usually two cardinals, besides two laterals on the ante-
rior side and one on the posterior side ; sockets deep : inside
more or less fluted, and having the margin notched.
This genus is redolent of the good old times. It
carries with it a smack of true conservatism— progressive
improvement without innovation. Every sound conchologist
must rejoice at seeing the name of Cardium
still preserved, with a few others, and to know that
they have survived the extensive and often injudicious
changes which systematists have been continually proposing
since the death of the much-honoured Swede.
Some corrections and modifications of his scheme of
classification were required by the progress of science,
and they have been made. With regard to our own
molluscan fauna, C. corneum, C. lacustre, C. amnicum,
C. rubrum, C. discors, and C. arcuatum of Montagu
have been placed in very different families, and a few
species have lately
been added to the British list. But
the genus has a solid foundation, and is likely to last as
long as conchology itself.
Its large and fleshy foot is admirably adapted for
penetrating and burrowing into sand. The mode by
which this operation is effected has been well described
bv Reaumur. He savs that when the animal wishes to
and at the same
sink, it lengthens its arm [or foot],
time attenuates the extremity of it, which thus becomes
almost pointed. With this it makes a hole, like a
gardener using his dibble, and buries the arm in the
sand, continuing the perforation with the pointed end ;
and by repeatedly lengthening and contracting this
muscular organ, it in a short time works the shell below