3. Genus Strombus. Pl. [XII].

Animal. Spiral; the foot rather wide anteriorly, compressed posteriorly; mantle thin, forming a prolonged fold anteriorly, whence issues a sort of canal; head very distinct; mouth a vertical slit at the extremity of a proboscis, provided in the inferior median line with a lingual band having prickles flexed posteriorly; tentacular appendages cylindrical, thick, and long, with the eyes at their extremity.

Shell. Thick, subinvolute, dilated in the middle, terminating in a cone anteriorly and posteriorly; aperture very long and narrow; terminated anteriorly by a canal more or less elongated and flexed; edges parallel, the external dilating with age, presenting posteriorly a gutter at its point of attachment with the spire, and, anteriorly, a sinus behind the canal, through which the head of the animal passes; operculum horny, long, and narrow; summit terminal. Found in the Indian and Equatorial seas, and one species in Florida. Thirty-two living species. Five fossil.

FAMILY XIX.
Purpurifera. Eleven genera.

1. Genus Cassidaria. Pl. [XII].

Animal. Somewhat elongated, widened anteriorly; mantle with simple edges and provided with a distinct tube; foot very wide, elliptical, sub-biolate anteriorly, and having a large operculum upon the dorsal face of its posterior part; head wide and indistinct; tentacula anterior, approximating at base, subcylindrical, and having the eyes at two-thirds of their length; mouth inferior, concealed by the foot; two pectiniform branchiæ, nearly parallel.

Shell. Subglobular, tuberculated or channeled, with a short, pointed spire; aperture long, ovate, subcanaliculated anteriorly; right edge folded back; columella covered by a wide, smooth callosity, uniting posteriorly with the right edge. Inhabits all seas except the Northern. Five living species. Seven fossil.

2. Genus Cassis. Pl. [XII].