the name given by French naturalists to a peculiar species of oysters, called also mollusca by others. It is one of the most curious shells in the world. Its figure is that of a hammer, with a very long head, or rather of a pick-axe. It has a body of moderate thickness, and two long arms. It is of a brownish colour, with a beautiful tinge of a violet-blue. Notwithstanding the strange shape of these shells, they close very exactly.