78 CONCHIFERA. MONOMYAIKA. 



Gen. 13. O&TREA, Lam. Lin. 



Shell adhering, ineqtiivalve, irregular, with beaks separated, and 

 the upper valve advanced as the animal increases in age ; 

 hinge without teeth ; ligament half internal ; the hollow of at- 

 tachment and the beak in the lower valve increasing with age. 



The shell of the Oyster, so well known, is composed of two unequal valves, of 

 which the upper is smallest and flat, while the under, adhering to marine bodies, is 

 larger and concave. It is rough, often scaly, and sometimes singularly plicated 

 at the margin. There is no teeth in the hinge, but an elastic ligament placed in 

 an oblong furrow under the beak. The upper valve is displaced and brought 

 forward as the animal increases in age. Oysters, of all testaceous animals, are those 

 which appear to possess the faculties of life in the lowest degree. Immoveably 

 fixed on rocks, or other marine bodies, they have no choice of food but what the 

 waves carry to them, and give no other sign of life than that of opening and shut- 

 ting their valves. 



* Margin of the valves simple or waved, not plicated. 

 O. edulis, Lin. Shell oblong orbicular, very rugged, with imbri- 

 cated transverse membranaceous wrinkles ; upper valve flat. Eu- 

 ropean coasts. Very common Browns Illust. pi. 31, fig. 19. 



The Oyster is well known as abundant on the coasts of Britain, where it has been 

 known from the earliest times, and from whence it was sent in quantities to the 

 epicures of ancient Rome. The Romans had their layers or stews for feeding oysters 

 for the table ; and in some parts of England this practice is continued. At some 

 former period oysters have been extremely plentiful in the Frith of Forth, and much 

 farther up that arm of the sea than they are taken at present ; for about a mile and 

 a-half above Borrowstounness, on the south side of the Forth, and distant from the 

 sea above a mile, is a solid bed of oyster shells several feet thick, and running along 

 the coast for a considerable distance. It is singular that no other species of shells 

 are found in this bed, except the lepades which are commonly found attached to the 

 shell of the oyster. 



O. Firginica, Lam. Shell oblong, thick, curved, with imbricated 

 transverse wrinkles, and the summit of the lower valve produced ; 

 margins very entire ; colour yellowish white. From 5 to 6 in- 

 ches long. Inhabits coasts of Virginia. Lister, pi. 201. fig. 35. 



** Margins of the valves distinctly plicated. 



O. cornucopice, Lam. Shell ovate, wedge-shaped; apex rounded; 

 margin below plaited ; lower valve with a rounded beak 

 Fava?me, pi. 45, fig. E. 



O. folium, Lin. Shell parasitical, oval, obtusely plaited on the sides 

 and transversely wrinkled ; colour tawny or straw colour. 1 1 inch 

 long. Inhabits Indian and American seas, on the roots of litto- 

 ral trees, &c. Rumph. Mus. pi. 47, fig. A. 



O. crista galli, Lam. (Mytilus, Lin.) Shell rounded, sharply plait- 

 ed and spinous ; margins rough ; colour reddish white, sometimes 

 violet. 21 inches long. Indian seas D'Argenv. pi. 20, fig. D. 

 The species of fossil oysters are numerous. For a descriptive list of those found 



in Britain see Fleming's British Animals^ pp. 393, 394. 



Gen. 14. GRYPH.EA, Lam. 



Shell free, inequivalve ; the lower valve large, concave, termi- 

 nated in a projecting beak, bentspirally ; the upper valvesmall, 



3 



