The Limpets dwell upon the sea-shore, in the parts alternately covered and uncovered by the waves. They are almost always attached to rocks, or other submerged bodies, to which they adhere with great tenacity. If the common Limpet (Patella vulgata) is alarmed before any attempt is made to dislodge it, no human force, pulling in a direct line, can remove it, and it can sustain without being crushed a weight of many pounds. It holds on by the great quantity of vertical fibres of the foot, which in raising the median part forms in the centre a sort of sucker. It is the celebrated experiment of the Magdeburg cups which these little molluscs realise by their vital action.
These animals bury themselves in the chalky rocks to the depth of two or three lines; when they are dispersed, they are observed constantly to return to the same place. Their movements are, besides, extremely slow; the advance of the Limpet being only perceived by watching the slow upheaval of the shell above the plane of its position. It is supposed, from the mouth being armed on its upper edge with a large semi-lunar, horny, cutting tooth, and in its lower part from having a tongue furnished with horny hooks, and from their inhabiting in great numbers places covered with marine plants, that their food is chiefly vegetable.
Fig. 212. Patella cærulea (Lamarck). Fig. 213. Patella umbella (Gmel.).
The poorer inhabitants of the coast eat limpets when they have nothing else, but their flesh is singularly coriaceous and indigestible.
They are found in every sea; but are, however, found to be larger as well as more numerous, and much richer in colour, in Equatorial seas, and especially in the southern hemisphere, than in European seas. They attain, in fact, their maximum of development here; for in the Straits of Magellan species are found as large as a slop-basin, which the natives use for culinary purposes.
The common Limpet is thick, solid, oval, and nearly circular, generally conical, and covered with a great number of very fine stripes. Its colour is of a greenish grey, uniform above, and of a greenish yellow inside. It is abundant in the Channel and on Atlantic coasts.
The Blue Limpet, Patella cærulea (Fig. 212), from St. Helena, has an oval shell, broadest behind, moderately thick, depressed, flattened, covered with angular wrinkles, and dentate on the edge. It is of a spotted green outside and of a fine glossy blue within.
Fig. 214. Patella granatina (Linnæus). Fig. 215. Patella barbata (Lamarck).