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Among the shells which abound in this cliff are Paludina lenta and various species of Lymnea, Planorbis, Melania, Cyclas, Unio, Potamomya, Dreissena, etc. Wood have found the jaws, teeth, and hard shining scales of the genus Lepidosteus, or bony pike of the American rivers. This same genus of fresh-water ganoids has also been met with in the Hempstead beds in the Isle of Wight.
They feed on the decaying leaves of the iris and other water plants, and from the number of divisions on the shell are believed to live for sometimes twenty years. Of the many varieties, one, the largest, the horn-coloured planorbis, emits a purple dye.
The mollusks abound, a peaceful tribe. At the bottom, the plump river snails discreetly raise their lid, opening ever so little the shutters of their dwelling; on the level of the water, in the glades of the aquatic garden, the pond snails Physa, Limnaea and Planorbis take the air.
All the well-known, usually very clear proofs from palæontology, comparative anatomy, &c., which we are accustomed to meet with in evolutionist books are wanting here, the genealogical trees of the Equidæ, with the gradually diminishing number of toes and the varying teeth, of Planorbis multiformis, of the ammonites, the graduated series of stages exhibited by individual organs, for instance, from the ganglion merely sensitive to light up to the intricate eye, or from the rayed skeleton of the paired fins in fishes up to the five-fingered hands and feet of the higher vertebrates, &c.
I have shown that there is a fluviatile deposit in the valley of the Niagara, containing shells of the genera Melania, Lymnea, Planorbis, Velvata, Cyclaz, Unio, Helix, etc., all of recent species, from which the bones of the great Mastodon have been taken in a very perfect state.
Several cases are on record of the same species presenting varieties in the upper and lower parts of the same formation. Thus Trautschold gives a number of instances with Ammonites, and Hilgendorf has described a most curious case of ten graduated forms of Planorbis multiformis in the successive beds of a fresh-water formation in Switzerland.
On the stems of water-lilies, on piles, on weeds and roots in any shallow streams, but always on the under side of the leaves, are the limpets of the Thames. The small ammonite-like shells are called planorbis, and like most of the others, belong also to the upper tertiary fossils.
Snails cling to the sides, and clean away and consume all this vegetable growth. The Lymnea is among the most efficient, but unfortunately is destructive, by eating holes in the young fronds of the larger plants, and thus injuring their appearance. To this objection some other varieties of snail are not open. The Paludina and Planorbis are the only kinds which are trustworthy.
For a vessel containing twelve gallons the following selection of live stock is among those recommended: Three Gold Carp, three Prussian Carp, two Perch, four large Loach, a dozen Minnows, six Bleak, and two dozen Planorbis. Some varieties of the Water-Beetles, or Water-Spiders, which the fishes do not eat, may also well be added. The Newt, too, is attractive and harmless.
Bembridge limestones, compact cream-coloured limestones alternating with shales and marls, in all of which land-shells are common, especially at Sconce, near Yarmouth, as described by Mr. F. Edwards. One of the bands is filled with a little globular Paludina. Anoplotherium commune. Binstead, Isle of Wight. Planorbis euomphalus, Sowerby. From this formation on the shores of Whitecliff Bay, Dr.
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