2. Genus Emarginula. Pl. [IX].

Animal. Body creeping, with two, conical, tentacular eyes at the external base; mantle large, partly covering the margin of the shell; foot very large and thick.

Shell. Shield-like, conical; summit inclined; the cavity simple, having a notch or hollow cut on its posterior margin; shells of this genus are generally very small. Inhabits the British seas. Five species.

3. Genus Fissurella. Pl. [IX].

Animal. With the head truncated in front; two conical tentacula, with eyes at their exterior base; mouth simple, terminal, and destitute of jaws; two pectinated branchiæ projecting from the cavity; mantle large, protruding beyond the shell.

Shell. Shield-shaped, conical recurved, summit entire, depressed, concave below, perforated at the summit in the form of a key hole, without a spire; the exterior surface ribbed longitudinally. Inhabits the European and American seas. Twenty-two species.

4. Genus Pileopsis. Pl. [X].