1. Genus Crenatula. Pl. [VIII].
Animal. Unknown.
Shell. Irregular, much flattened, subrhomboidal, subequivalve, gaping posteriorly; summit anterior; hinge longitudinal, dorsal, toothless; ligament submultiple, or inflated from place to place, and inserted in a series of round cavities corresponding with the dorsal edge; muscular impression unique and subcentral. Inhabits the Red Sea. Seven species.
- Crenatula modiolaris.
- C. avicularis.
- C. nigrina.
- C. bicostalis.
- C. viridis.
- C. mytiloides.
- C. phasianoptera.
2. Genus Perna. Pl. [VIII].
Animal. Body much compressed, the mantle prolonged posteriorly in a sort of lobe, and fringed at its inferior edge only; a byssus; a single contractile muscle.
Shell. Irregular, much compressed, subequivalve, form somewhat variable, gaping at the anterior part of its inferior edge; summit very small: hinge straight, vertical, buccal, toothless; ligament multiple, and inserted in a series of longitudinal and parallel furrows; a subcentral muscular impression. Inhabits the Indian seas. Ten species living. Two fossil; one found in France and one in Virginia.
- Perna ephippium.
- P. isognomon.
- P. femoralis.
- P. marsupium.
- P. obliqua.
- P. sulcata.
- P. vulsella.
- P. nuclea.
- P. avicularis.
- P. canina.
3. Genus Malleus. Pl. [VIII].
Animal. Imperfectly known, but certainly byssiferous, with a single retractile muscle.