ostraceous

That in the smaller jar is of the least consequence, being a mere unconnected formless fragment of a brown colour; while the other (which is figured) as grown over the concavity of a small ostraceous bivalve shell (fig. 26, b), and is of a lighter colour, but at once reveals the structure and habitat of the sponge, although, from being only a fragment with none of the surface left, it fails to afford its general form.