The umbilicus of the shell is often completely covered with a thick and smooth callus.

[3] The animal has a distinct lateral fringe of the foot, with three filaments on each side.

The front of the right side near the base of the tentacles is produced into a fleshy lobe.

The right tentacle is free, with the eye-peduncle compressed, and bears a rudimentary eye.

The left eye-peduncle is cylindrical, with a distinct eye, and furnished with an expansion or frontal lobe, which is folded on itself and fringed at its free margin.