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. [Illustration] 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 [Illustration] THE WHELK, A univalve shell inhabited by a gasteropod mollusk, or, we should rather say, naturally so tenanted, for very frequently it is taken possession of by the Soldier or Hermit Crab, which having no hard covering to protect their soft plump bodies, are obliged to take lodgings where they can get them, and generally prefer the Whelk shell, of which we here give a figure. [Illustration]