Shell ovate, above rather depressedly conical, beneath concave; vertex, when not eroded, obliquely turned backwards, exactly in the opposite direction to the canal, which is on the right side. Within, the muscular impression is observable; it is commonly very distinct, and nearly surrounding the inside at rather less than halfway from the edge to the lowest point; interrupted in front by the head of the animal, and on one side by the canal, so that between the canal and the head, there is an irregularly subcircular muscular impression only connected with that of the other side of the shell by a very narrow line, over which lies the head of the animal; the extremities of the muscular impression are rather expanded, particularly that immediately behind the canal. The canal itself sometimes forms a distinct groove within the shell, running from the vertex to the margin, and a corresponding prominence may be observed on the outside, forming a ridge from.the vertex to the margin; but the internal groove and the external ridge are not always distinct; the place of the head and that of the canal can, however, be easily distinguished in all cases. (Sowerby.)

Cape, India, Philippines, Australia, New Zealand. Pacific, Galapagos. Peru, Cape Horn, California. Fossil: Miocene . . . .