River and land shells are generally very thin and brittle, and must be carefully handled; their colours are not usually so brilliant as those of the marine species, but they form links in the testaceous chain, which are necessary to a proper study and elucidation of conchology. The most glowing and gorgeous of all shells are those brought from the Tropical seas, and, excepting in a few rare instances, specimens of most of these can be obtained at little cost from any dealer, or from sailors returning from a voyage. If it is necessary to send either those, or British shells, any distance, or to pack them away in a small compass, the best plan is to wrap them separately in soft paper, place them in a box, and then pour in sawdust, bran, or fine sand, very dry, until all the open spaces are completely filled up. ON CLEANING AND POLISHING SHELLS. All shells, whether inhabited or not, when taken should be soaked for a while in hot water, to remove the dirt which may adhere to them, and dissolve the saline, that is salt, particles contained in the sea water; they should then be thoroughly dried, and if, as is the case with many, they naturally possess a good polish, they are at once fit for the cabinet. Generally, however, it happens that when shells are dry, they lose much of the peculiar brilliancy of hue, which they possess when seen through the medium of the glistening water; to restore this, wash them over with a thin solution of gum arabic, or white of egg; some collectors use a varnish made of gum mastic, dissolved in spirits of wine; this is perhaps preferable, as it is not affected by moisture. Many shells have a very plain, dull, appearance, in consequence of being covered over with a kind of skin called an epidermis, a word derived from the Greek, and signifying the outer skin, sometimes called the cuticle. To remove this, soak the shell in warm water for some time, and then rub it over with a stiff brush until the covering is removed; should this be very thick, it will be necessary to mix a little nitric acid with the water, but this must be done very cautiously, for if too strong it will remove all the lustre from the surface of the shell subjected to its influence. Sometimes the file, and a substance called pumice stone has to be used, but these are dangerous agents in inexperienced hands. The best polish for the shell after the skin is removed, is a red earth called tripoli, applied on a piece of soft leather. FOSSIL SHELLS.