The Iris Ear-Shell, ([Haliotis Iris].)
The Haliotides, or sea-ears, are very splendid shells; the species are numerous, and some of them are extremely common. The place in the system which this shell ought to occupy, appears to have caused many doubts in the minds of modern naturalists, and consequently, we find it continually shifted from one part to another in the different works of Lamarck and Cuvier. When moving from place to place in search of food, the animal and its shell present a very pleasing sight, the slender tentacula which appear through the different holes which ornament the margin of the shell, gracefully waving in all directions; these tentacula are supposed to be breathing-tubes. In the young shell, the number of perforations is not so great as in an adult, one being formed at each progressive stage of the creature’s growth. Sometimes the holes which were first formed become, by age, filled up. The proportions of the shell, also, vary materially, so as to render the separation of species very difficult and uncertain.
The Dusty Neritina, ([Neritina pulligera].)
This shell is found in the rivers of India, and is about an inch and a quarter in length. All the species of this genus are supposed to inhabit fresh water only. There is a curious fact attached to the history of the Neritina, and of a neighbouring genus, Nerita,—namely, that when found in a fossil state, their colours are always in good preservation. The species, which are tolerably numerous, are in general natives of hot climates.
The Viviparous Paludina, ([Paludina vivipara].)
The animal of the genus Paludina is an inhabitant of fresh waters: it takes its specific name from the fact of the young being hatched within the parent shell, and deposited in the waters perfectly formed. In nearly the whole of this class the eggs are laid either in water or in the earth, and afterwards hatched after a longer or shorter period.
Planorbis corneus.Paludina vivipara. Lymnæa stagnalis.
These shells are found generally in running streams of fresh water; sometimes, however, they are met with in brackish water, at the mouths of rivers. The operculum of the Paludina is of a strong horny substance. The young, immediately they are hatched, attach themselves to the outside of the shell of the mother, where they remain until they are sufficiently strong to trust themselves in the water.