“Shells having the general form, of Productus, but uniformly with a narrow area on each valve, a foramen or callosity on the ventral area, small teeth, and more or less distinct teeth-sockets. The reniform vascular impression, rising from between the anterior and posterior occlusor muscular impressions, curves gently outwards, and, following a curvature somewhat parallel with the margin of the shell to below the middle of its length, is abruptly re-curved, and the extremity, turned a little backwards, terminates about halfway between the margin and the anterior extremity of the mesial septum. The cardinal process, seen from the inner side, is bilobed, and from the exterior side each of these divisions is usually bilobed.