FRESH-WATER SHELLS.
Many of the following group of Fresh-water Shells, are remarkable for elegance of form, and some for richness of colouring; hence, perhaps, the scientific name applied to the family in which they are mostly included—Limnæidæ, which, like limn—to paint, agrees with the French enluminer. These mollusks are found in rivers, streams, ditches, and moist marshy places. Like those which live wholly on land, they breathe through lungs, and therefore cannot exist without air; which accounts for their frequently coming to the surface, when under water. In brooks, as well as in stagnant pools, which abound with aquatic plants, they may be found in vast numbers, feeding upon the moist vegetation.
The Common Limnea, (L. stagnalis,) is mostly an inhabitant of stagnant waters, where it is often seen floating with the shell reversed, as in a boat; this shell, like most of those of the Fresh-water Mollusks, is thin, and easily broken; the shape it will be seen, is peculiarly elegant, the spire being slender and pointed—very different from that of the Spreading Limnea, called by naturalists, L. auricularia, from aurus—the ear, to which the broad aperture, or opening of the shell, may be compared; this resembles the other species in its habits. The Horny Planorbis, in Latin P. corneus, from cornu—a horn. The shape, you will see, is flat, the whorls rolling upon each other like the folds of a bugle horn; this shape would be termed orbicular, from orbis—a sphere, or circular body. This is the largest European species of Fresh-water Shells so constructed; it is often found in deep clear ditches, and yields a beautiful purple dye, which, however, soon becomes dull, and changes; it cannot be fixed, and is therefore valueless. The mouth of this shell in fine specimens, is tinged with pale violet or lilac.
There is another kind, the Keeled Planorbis, (P. lurinatus,) which has the outer edge of the shell finely ridged, or keeled; it is very small, and very plentiful in fresh-water, both running and stagnant; where, too, is found the Common Physa, (P. fontinalis,) the latter word meaning a spring or fountain. This little mollusk is a quick and active traveller, it sometimes comes out of its shell, and throws itself about in an extraordinary way, keeping fast hold by its foot; the generic name, Physa, would seem to have reference to the round, smooth, delicate shell, and to come from the same root as Physalite, which means a topaz: the members of this genus are very numerous, being found nearly all over the globe. The next belongs to the family Auriculadæ, or Ear Shells. The Midas’ Ear, (A. Midæ;) this handsome shell is prized by collectors; it comes from the East Indies. Midas, it is said, was one who set himself up for a judge of music in the old fabulous times, and not appreciating that of Apollo, was rewarded by the angry god with a pair of ass’s ears.
The Cone-shaped Melampus, (M. corniformis,) also an Ear Shell, is found in the rivers of the Antilles Islands. It is a pretty shell; the formation is much the same as that of many of the most highly-prized varieties of Marine Shells; of these we shall have to speak presently. Melampodium in Latin, signifies a poisonous plant called Black Helebore; in the Mythology, Melampus was a great magician, who did all sorts of wonderful things; but we cannot tell what relation there exists between either the plant or the magician and this pretty cone shell. To give variety to this group, we will now throw in a land species called Megaspira Ruschenbergiana, about the origin of whose name we cannot even hazard a guess; the termination of the generic name, you will see is spira, and a glance at the shell will at once suggest a reason for this; its long tapering spire consists of twenty-three closely-set gradually increasing whorls. This is a rare shell, whose inhabitant has not yet been described by naturalists; several of the marine species closely resemble it in shape. Much more might be said about the Land and Fresh-water Shells, but we must here leave them, having a wide field before us, namely, the Sea or Marine Testacea, one of the most common of which is
