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.