Animal. Spiral, with the foot (which is shorter than the shell) rounded anteriorly; mantle provided, before the respiratory cavity, with a long open canal, used as an organ of prehension; head furnished; a single pair of blackish tentacula, having the eyes at an inflation about half way from the base; mouth armed with a proboscis.

Shell. Inflated, oval, subinvolute; spire slightly projecting; aperture long, oval, sometimes very narrow, terminated anteriorly by a very short canal, sloped, and flexed obliquely towards the back; columella covered by a large callosity, indented throughout its length; operculum horny. Found in the Indian, Mediterranean, and Equatorial seas. Twenty-five living species. Eight fossil.

3. Genus Ricinula. Pl. [XII].

Animal. As above.

Shell. Oval or subglobular, thick, armed with points and with a depressed spire; aperture narrow, elongated, notched, sometimes canaliculated anteriorly and digitated exteriorly; left edge more or less callous; operculum horny, oval, and transverse. Found in the Indian seas. Nine living species.

4. Genus Purpura. Pl. [XII].

Animal. As above.

Shell. Oval, tuberculated, thick; spire short, the last whorl much larger than all the others united; aperture oval, greatly dilated, terminated anteriorly by a short, oblique canal notched at the extremity; the columellar edge nearly straight, covered with a callosity; operculum horny, flat, nearly semicircular, with faintly marked transverse striæ. Found in the European and South American seas. Sixty-two species.