species of the same genera are never or rarely seen in gardens, but devour the herbage of the roadside, the bank, or the hedge. Many, particularly those which inhabit the woods of foreign countries, devour the leaves of trees. The plant-eaters among the marine tribes live upon the various kinds of sea-weeds, of which there is a sufficient variety to gratify a taste much more epicurean than it probably is in reality. The common Periwinkle and the Limpet are both vegetable feeders, and there is a pretty little species of the latter genus which invariably, I believe, confines itself to one plant: this is the Patella pellucida, distinguished by having on its summit three or four lines of blue, most brilliantly gemmeous. It feeds on the tangle, (Lammaria digitata) eating away a cavity for itself, just large enough to contain its body, in the substance of the cartilaginous stem, commonly beneath the shelter of the arching roots. I have pulled up the tangles by dozens at low spring-tide, and have scarcely ever found one that had attained certain dimensions without finding a little parasitical Limpet embedded in its substance.
If we measure the interest which we take in any section of created beings by their powers of conferring benefit or inflicting injury on our own race, we shall find the Mollusca not unworthy of our regard in both these respects. Many of them are used as human food, and that not by savage nations only, but by ourselves and by all classes of society. The Limpet, the Periwinkle, the Whelk, the Mussel, and the Cockle, are commonly sold in the streets of our sea-port towns and large cities, though these are certainly more prized by the lower classes of society than by those of more cultivated tastes.