Glycimeris siliqua.
G. siliqua. The podlike Glycimeris.
Transversely oblong, covered with a black epidermis; umbones decorticated; internal disc of the valves white, thick, and callous.
FAMILY IV.
Myaria. Two genera.
1. Mya. The Trough Shell, or Gaper. Four species.
This term is derived from the Greek word μυω, to close, alluding to the animal’s custom of closing the valves. The principal characteristic of the Mya is its gaping at one end; it is likewise distinguished by having a large spoonlike tooth proceeding from beneath the beak. Its form is greatly varied, but generally covered with a greenish epidermis, which may be removed; and the shell, when polished, will display beautiful prismatic colours. The Mya is found on the seashore or on the banks of large rivers, partially concealed in the sand and mud.
Shell transverse, inequilateral, surrounded with a thick epidermis; rather solid; edges thin and sharp; summits but little marked; hinge dissimilar; one or two large, compressed, spoon-shaped teeth rising perpendicularly from the plane of the left valve, and fitting into the entrance of a primary cavity in the right valve; ligament interior, attaching the tooth and cavity; two distant muscular impressions; the anterior long and narrow, the posterior rounded; the mantle impression narrow, with a large sinus or hollow.
Mya truncata.
M. arenaria.
M. erodona.