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From the usual form of the orifice in the shell of this genus, which resembles that of a key-hole, the species are familiarly known by the appellation of Keyhole Limpets. It is placed at the summit of the shell, which is very regularly conical, and not otherwise to be distinguished from that of a Patella. In the very young condition the orifice is placed more forward. The animal has been already sufficiently described.

FISSURELLA RETICULATA.

We have but a single native species, the Netted Keyhole Limpet (Fissurella reticulata). It attains an inch in length, is of an oval form, and of a dirty white hue, with dusky rays. Its surface is sculptured with a raised network, formed by radiating and circular ridges. The animal is large, and of a yellow colour, varying in shade from cream-white to a rich deep orange; the latter hue being seen only in those specimens that are found adhering to shells incrusted with a scarlet sponge. It is obtained only on our western and southern coasts.