This genus received its name from its resemblance to a heart (καρδια).
It is so well defined by Linnæus that no alteration was made by Lamarck,
except in making two divisions of them; the first distinguished by
having the anterior side as large or larger than the posterior, and no
distinct angle at the apex; the second by possessing carinated or
angular umbones, and the posterior side often much larger than the
anterior. These shells are found at a small depth in the sand on almost
every seashore.
Shell inflated, equivalve, sub-cordiform (when seen anteriorly),
generally costated from the summit to the circumference; summits very
evident; slightly recurved forward; hinge complex, similar, formed by
two oblique cardinal teeth, articulating with the corresponding teeth on
the other valve; two distant lateral teeth on each valve; ligament
dorsal, posterior, and very short.
Cardium costatum.
C. Indicum.
C. ringens.
C. Asiaticum.
C. tennicostatum.
C. fimbriatum.
C. pseudolima.
C. aculeatum.
C. erinaceum.
C. tuberculatum.
C. Brasilianum.
C. apertum.
C. papyraceum.
C. bullatum.
C. ciliare.
C. echinatum.
C. lævigatum.
C. biradiatum.
C. eolicum.
C. pectinatum.
C. isocardia.
C. muricatum.
C. angulatum.
C. marmoreum.
C. elongatum.
C. ventricosum.
C. rugosum.
C. sulcatum.
C. serratum.
C. unedo.
C. medium.
C. fragum.
C. retusum.
C. tumoriferum.
C. rusticum.
C. edule.
C. Groenlandicum.
C. latum.
C. crenulatum.
C. exiguum.
C. minutum.
C. roseum.
C. scobinatum.
C. hemicardium.
C. cardissa.
C. inversum.
C. Junoniæ.
C. lineatum.
_C. edule._ The edible Cardium, or common Cockle. Pl. 10, fig. 2.
Species not gaping, with about twenty-six depressed ribs and transverse
obsolete scales; of a cream colour; beaks protuberant.
_C. cardissa._ Venus’s Heart.
Species heart-shaped, valves angularly flattened, umbones alternating.
_C. lævigatum._ The smooth Cardium.
Species smooth or nearly so, anterior side as large as the posterior.
_C. hemicardium._ The half-heart Cardium.
Species ribbed, with elevated rough striæ; the anterior side is very
short and almost flat.
_C. costatum._ The high-ribbed Cardium.
No angle at the umbones; anterior side at least as large as the
posterior; rows of white, hollow, elevated ribs, situated at regular
distances, proceeding from the umbones to the margin, with the spaces
between them of a reddish brown colour.
_C. unedo._ The Strawberry Heart.
Species with ribs armed with small crescent-shaped scales.
_C. tuberculatum._ The tuberculated Cardium.
Species not gaping, with large ribs armed with nodules.