BIVALVES. OSTREA. 55 



allied to the common or eatable oyster. The species of 

 this division are of a much more irregular form than the 

 scallops, and are usually very rugged, unfinished looking- 

 shells. The hammer oyster, O. malleus, is perhaps the 

 most remarkable of this class; its form resembles that 

 of a long-headed hammer, or more properly a pick axe: 

 there are two distinguishable varieties of it, viz. the white 

 and the black, both of which, when in fine preservation, 

 are considered rare and valuable. These shells are rough 

 and plaited on the outside, but their inside is smooth and 

 glossy, having a steel-blue color or metallic lustre diffus- 

 ed over the surface. 



The hinge of some of the species, as the O. perna and 

 O. isognomon, has a perpendicular grooved line attached 

 to it. Some, again, as the O. vulsella, &c. gape at the 

 hinge; others terminate in a long beak from the hinge 

 upwards, as the O. cornucopiae and O. virginica. Some 

 species have the appearance of a dried leaf, such as the 

 O. folium, &c. this species often grows to the roots and 

 stumps of trees, especially the mangrove, and is also found 

 affixed to the gorgoniee. 



The common oyster (O. edulis) is too well known for 

 its nutritious and palatable properties to require much de- 

 scription ; suffice it to say, that the exterior of the shell 

 is usually covered with undulated and imbricated scales, 

 of a yellowish or pinkish olive cast; and the old shells are 

 often covered with various adhesions, such as anomiac, 

 serpulae, lepades, sertulariae, and other marine produc- 

 tions. The interior of the shell has generally a pearly 

 appearance, and specimens are often found containing 

 pearls. They are to be met with in most seas, occasion- 

 ally in clusters, affixed to rocks and other substances* 

 In some places they are considered so profitable a branch 



