5. Genus Monoceros. Pl. [XII].

Animal. As above.

Shell. Differs only from the Purpura by a long, conical pointed, somewhat reflexed tooth in the outer lip. Five species.

6. Genus Concholepas. Pl. [XII].

Animal. Entirely unknown.

Shell. Wide, rough, ovate; spire very short; aperture very large, oval and sloped anteriorly; the edges united, the right very thick and dentated; muscular impression almost in form of a horse-shoe; operculum horny and rudimentary. It was formerly considered a Patella, from which it differs by the operculum. One species.

7. Genus Harpa. Pl. [XII].