OSTRACITES, in natural history, a name used for the fossil oysters, common in many parts of England. They are of various shapes and kinds; and the name is by some authors made to signify the shell itself, when preserved in its native state and condition; as is the case with those about Woolwich and Blackheath; and by others, the stones cast or formed in those shells, or in cavities from whence they have been washed away and dissolved: in both these cases the stone carries the exact resemblance of the shell, even in its nicest lineaments; in the first case, bearing every mark of the inside, in the other of the outer surface. We have this stone in great plenty in many parts of England; and it is very famous, in some places, for its virtues in cases of the gravel, and the like complaints.