_S. radiatus._ The radiated Solecurtus. Species flat, small, with an interior ridge running down obliquely from the summit to the abdominal margin. _S. strigilatus._ The strigilated Solecurtus. Species more cylindrical, without interior ridge. _S. legumen._ The Pease-pod Solecurtus. Pl. 31, fig. 6. Species still more elongated and sub-cylindrical. 4. Glycimeris. Two species. Distinguished from the Solen by being without teeth at the hinge. Shell covered with epidermis, slightly irregular, elongated, gaping at the two extremities, equivalve, inequilateral; the summits but little marked; hinge toothless; a longitudinal callosity; ligament exterior, affixed to very projecting callosities on the shortest side of the shell; two distinct muscular impressions. Glycimeris margaritacea. 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. M. solenimyalis. _M. arenaria._ The Sand Mya. Pl. 5, fig. 1. Regular species. _M. erodona._ The Erodona Mya. Irregular species, in which the cavity of the right valve is bordered by strong projections. _M. truncata._ The truncated Mya. Pl. 5, fig. 3. Sub-oval, truncated; small end gaping; large end rounded; covered with a dark yellowish epidermis; inside white; wrinkled transversely. 2. Anatina. The Duck’s Bill. Ten species.