FAMILY X.
Cardiacea. Five Genera.

1. Genus Cardium. Pl. [VII].

Animal. Body somewhat inflated; mantle edged with tentacular cirri in all its inferior part; tubes united, of moderate size, and provided with cirri at the extremity; mouth transverse, very wide, with moderate labial appendages; foot very large, cylindrical, somewhat inclined anteriorly; branchiæ thick, rather small, especially the external laminæ: the internal united in all their extent.

Shell. Inflated, equivalve, sub-cordiform (when viewed anteriorly, usually costated from the apex to the circumference); summits very evident, but slightly flexed to the front; hinge complex, similar, formed of two oblique, conical cardinal teeth, and of two distant lateral teeth, upon each valve; ligament dorsal, posterior and very short. Inhabits the European and American seas. Fifty-seven living species. Fourteen fossil.

2. Genus Cardita. Pl. [VII].

Animal. Body suborbicular, terminated superiorly by a sort of hook; mantle but little open; foot terminated at its extremity by a part much narrower than the base; superior lobes of the branchiæ very short.

Shell. Thick, solid, equivalve, more or less inequilateral; summit dorsal always much flexed anteriorly; hinge similar, formed by two oblique teeth, one short, cardinal or apicial, the other postapicial, long, lamellous and arcuated; ligament elongated, subexterior and inserted; two very distinct muscular impressions, united by a palleal band, narrow and semicircular. Inhabits the Mediterranean and American seas. Twenty-three living species. Four fossil.