Lymnæa Stagnalis.
The [Lymnæa stagnalis] is found in stagnant waters, particularly narrow ditches, in great abundance. As it breathes air, it is necessary for its existence that it should frequently resort to the surface of the water; and consequently, we find these shells floating about in great numbers, with the body partly out of the shell. The least appearance of danger causes a Lymnæa to withdraw the whole of its body into its shelly covering; and as this increases its specific gravity, it instantly sinks to the bottom, where it remains in safety. In order to reach the surface again, it is obliged to crawl to the side of the ditch, and when it has reached the level of the water, it again trusts its little bark to the mercy of the winds and stream, for it has very little power to direct its own course.
During the Winter, these creatures remain at the bottom, buried in the mud, and in a state of torpor. Although apparently useless to mankind, they form part of the subsistence of many water-birds, and of fishes, which are extremely fond of them. The species of this shell are not easily decided, since they bear so great a resemblance to each other.
The Horn-shaped Planorbis,
([Planorbis corneus].)
The Planorbis, although differing in form from the Lymnæa, possesses the same habits, and is found in the same localities. The jelly-like substance which is frequently found, in the Spring of the year, attached to water-cresses and other aquatic plants, and which is considered by many to be of a poisonous nature, and looked on as the spawn of toads, is merely the covering of the ova of this and other inhabitants of fresh-water shells; and, although very disagreeable, certainly not poisonous.
The Red-mouthed Bulimus, ([Bulimus hæmastomus].)
The Bulimus hæmastomus is a most beautiful shell; it is a native of Guiana, and is frequently as much as four inches in length. The most singular part of its natural history is the large size of the egg of the animal in comparison with its magnitude; it is said to equal that of a moderate-sized pigeon.
Bulimus hæmastomus. Pupa mummia.