right, for these creatures subsist on vegetable matter only, and if a goodly number be thrown in, they will be found perpetually at work, eating the green growth from the sides, and thus constantly preserving an open prospect.
Objections to Mollusks.—In a highly ornamental tank, water-snails may be thought objectionable, as interfering somewhat with the beauty of the scene. I know the ardent naturalist will cry out against this remark, and ask me if I can find a prettier object than a Planorbis corneus, coiled round like a horn of plenty; or a full-grown Paludina with its globular hybernaculum richly bronzed and mottled. I tell my friend that I love the pretty creatures as much as he does, yet, as I write for everybody who wishes to keep an aquarium, I feel bound to consider how it is to be managed without them, if their absence is desired. I confess too, that I do object to their appearance in some cases myself, as I do also to beetles, and all other insects in a tank fitted up for the adornment of a drawing-room, however necessary they may be in the tank of a student.
In the first place, Paludinæ and Planorbis are the only kinds to be trusted in a general collection of plants, and the last is most trustworthy of any. Lymnea are all fond of substantial dishes, and eat as much vallisneria as they do of the mucuous growth. A dozen of these gentry will most effectually check the vegetation of the tank, by eating holes in the handsomest leaves of the Stratoides, and biting into the very heart of the Vallisneria. Starwort, too, they are very fond of, and soon clear the bottom of every fragment. Yet, the Lymnea are admir-
