Fossil Bivalve Shells.
Fig. 1. A fossil Oyster (Ostrea Marshii, of Sowerby), from the Cornbrash of the Oolite, Wiltshire.
Fig. 2. The fossil Cockscomb Oyster, (Ostrea carinata, of Lamarck,) from the Lower chalk, Havre, France.
Fig. 3. The elegant fossil shell here figured is a peculiar and most abundant species in the Lias formation; specimens are not uncommon, in which every part of the shell is as perfect as if just thrown up on the sea-shore. It belongs to the genus Gryphites (Gryphea incurva, of Sowerby,) the shells of which are nearly related to the oysters, but are distinguished by the deep concave under-valve, and its curved beak, and the almost flat upper shell. The testaceous substance is of a finer laminated structure than in the Ostrea, and the hinge-ligament is inserted in an elongated curved groove.[61]
[61] Medals of Creation, vol. i. p. 387.
Fig. 4. "Ostrea vel frons folium."—Mr. Parkinson. This species appears to be the Ostrea gregarea (?) of Sowerby, which occurs in the chlorite marl or firestone of the Lower chalk in Sussex and Kent.
Fig. 5. The fossil is the cast of an oyster-like bivalve, called Perna, (Perna quadrata, of Sowerby,) which is easily recognisable, even in casts, by the line of distinct teeth which compose the hinge. This species is abundant in the Portland limestone, particularly in the quarries around Swindon, in Wiltshire; but from the close adhesion of the outer surface of the shell to the surrounding stone, they can seldom be extracted, the casts only being readily obtainable. In the Kimmeridge clay, which lies above the Portland rock, the shells may be met with in great perfection. The best locality is near Hartwell, in Buckinghamshire, where the clay is extensively dug for the brick manufactures.
Figs. 6, & 7. Two views of a small shell of the genus Crenatula, from Bedfordshire.
Fig. 8. Portion of a very large species of Perna (Perna maxillata, of Sowerby), from tertiary strata. Piedmont. The figure shows the inner surface of the shell with part of the broad crenulated hinge.