T. serrifera.
T. gigas. The giant Tridacna. Pl. [12], fig. 3.
Species of which the shell is sometimes very large, white, transversely ovate or elongated; the anterior side longer than the posterior; broad ribs covered with vaulted scales; when of a pink or orange colour, greatly valued.
2. Hippopus. One species.
Similar to the Tridacna, but distinguished from it by having its posterior slope closed with a dentated margin; its ribs are never arched or vaulted, and its anterior side is shorter than the posterior side.
H. maculatus. The spotted Hippopus. Pl. [12], fig. 1.
Shell transversely ovate, ventricose, with scaly ribs; lunule, heart-shaped, and oblique; margins deeply crenulated; reddish purple spots.
FAMILY XVI.
Mytilacea. Three genera.
1. Mytilus. The Muscle. Thirty-five species.
As arranged by Lamarck, now comprises only such shells as are regular, equivalve, and longitudinal; solid in substance, and attached to other bodies by a short thick byssus.