Testa opaca, læviuscula. Cardo nullis dentibus instructus, sed fossula
obliqua intra marginem.
This definition very properly excluded the oysters which had been
erroneously inserted in this genus. Only the _Mytili_ and _Modiolæ_ of
Lamarck were left as members; for _margaritiferus_ and _hirundo_ were
transferred to _Ostreum_!!