Pvn H,i I'UitlS

CARDIUM. 2G7
the surface. When, on the contrary, the animal would
return to the light, it is only necessary to expand and
press its arm firmly against the sand, and the shell will
rise in proportion to the power exerted from beneath,
and will soon be disengaged. By this means the cockle
is also enabled to move both forwards and backwards,
but in a very limited degree. So far Reaumur. I
may also observe that the sand in which it lives is always
more or less saturated or infiltrated with water, and
sometimes is even semifluid, making it much easier for
the cockle to work its way than if it had to penetrate a
harder mass. The foot is very elastic ; and the pro-
digious leaps
which the animal makes with it have been
noticed by many writers on popular science : Mr.
Gosse gives an amusing account of the feats which his
" Signor tuberculato " (C. tuberculatum) performed in
this way. The ridge-and-furrow sculpture is very re-
gular, and by means of this alternate arrangement each
valve locks closely into the other. Owing to the ad-
ductor muscles being but slightly attached to the shell,
the animal immediately becomes loose when put into
boiling or scalding water. Collectors therefore experience
no trouble in cleaning the inside of any cockle-
shell. For this reason also live cockles are much more
easily opened than oysters, the latter operation being
rather an arduous undertaking to a bungling tyro.
They may have served to illustrate the proverb mentioned
by Hesiod— Koy^rjv htekelv— signifying any slight
task.
Very many species of Cardium occur in a fossil state.
Mr. Searles Wood "
says, Species possessing uu doubted
characters of this genus have been obtained from the
middle secondary formations, and they are largely deve-
N 2