Species slightly oblique, somewhat square, pearly, very thick, compressed; undulated and transversely striated, with a series of lamellated longitudinal scales; exterior greenish, interior pearly. This shell is celebrated for its irridescent colours, and is valued for the beautiful and costly pearls it produces. These pearls are formed from a deposition of the substance destined to line the shell upon sand or other bodies, casually or purposely introduced within the mantle of the animal; the shell itself is the mother-of-pearl used for inlaying, or making various elegant trinkets.
FAMILY XVIII.
Pectinides. Seven genera.
1. Pedum. The Shepherd’s Crook. One species.
The common name was given to this genus from the resemblance to a French shepherd’s crook. The shell is of a regular form; its lower valve, in which is a sinus for the byssus, is turned up at the edges, and the upper valve falls within it.
Shell inequivalve, a little eared; apices unequal, distant, rounded, little evident; hinge without teeth; ligament inserted in an oblique groove, prolonged to the summit, and carried within in a kind of spoonlike cavity.
P. spondyloideum. The spondylus-shaped Pedum. Pl. [15], fig. 5.
Ovate, wedge shaped, flat; superior valve with longitudinal striæ; white, granulated, and rough; slightly tinged with purple near the beak.
2. Lima. The File Shell. Six species.
No sinus or notch; the valves, thick and gaping, form a lateral opening; the ears are small, but distinct.
Shell oval, more or less oblique, almost equivalve, with small ears, regularly gaping at the anterior part of the lower edge; summits anterior and distant; hinge longitudinal, without teeth; ligament rounded, almost exterior, inserted in a cavity of each valve; central muscular impression divided into three very distinct parts.