6. Genus Spondylus. Pl. [IX].

Animal. Body moderately compressed, provided inferiorly with a rudiment of a foot, without byssus; mantle open in all its inferior and superior portion; mouth surrounded with very thick and fringed lips.

Shell. Solid, adhering, subregular, more or less spined, subauriculated, inequivalve; the right or inferior valve fixed, much more excavated than the other, and having posteriorly at the summit a triangular face enlarging, and elongating with age; hinge longitudinal, provided in each valve with two strong teeth entering corresponding cavities; ligament short, nearly median, partly exterior; muscular impression single and subdorsal. Found in all the seas of hot climates, and even in the Mediterranean. Four or five fossils are found in France, one in South America. Twenty-one species.

7. Genus Podopsis. Pl. [IX].

Animal. Unknown.

Shell. Subregular, somewhat thick, equilateral, symmetrical, inequivalve, adhering by the extremity of the shorter valve; the other terminating in a pointed, reflexed, and median summit. Two fossil species.

FAMILY XIX.
Ostracea. Six genera.

1. Genus Ostrea. Pl. [IX].

Animal. Body compressed, more or less orbicular; edges of the mantle thick, not adhering or retractile, and provided with a double row of short and numerous tentacular filaments; two pairs of elongated and triangular labial appendages; a subcentral bipartite muscle.