It will be observed that in the foregoing allusions to organic remains, the testacea or the shell-bearing mollusca are selected as the most useful and convenient class for the purposes of general classification. In the first place, they are more universally distributed through strata of every age than any other organic bodies.

If I had worked my way from a sponge instead of a lobster, I should have found it associated, by like ties, with a great number of other animals into the sub-kingdom 'Protozoa'; if I had selected a fresh-water polype or a coral, the members of what naturalists term the sub-kingdom 'Coelenterata', would have grouped themselves around my type; had a snail been chosen, the inhabitants of all univalve and bivalve, land and water, shells, the lamp shells, the squids, and the sea-mat would have gradually linked themselves on to it as members of the same sub-kingdom of 'Mollusca'; and finally, starting from man, I should have been compelled to admit first, the ape, the rat, the horse, the dog, into the same class; and then the bird, the crocodile, the turtle, the frog, and the fish, into the same sub-kingdom of 'Vertebrata'.

In the whole of the English Lias there are at present known about 937 species of mollusca, and of these 267 are Cephalopods, of which class more than two-thirds are Ammonites, the Nautilus and Belemnite also abounding.

In the last edition of Sir Charles Lyell's "Elementary Geology" it is stated, on the authority of a former President of this Society, the late Daniel Sharpe, that between 30 and 40 per cent. of the species of Silurian Mollusca are common to both sides of the Atlantic.

What difference in rank, for instance, is there between an oyster and a cuttle-fish? between a cochineal and a bee or ant? and yet the first two belong to one and the same type the type of mollusca; and the last three to one and the same class the class of insects.

The several above-enumerated species of mollusca, which are found strewed on the surface of the land from a few feet above the level of the sea up to the height of 1,300 feet, all now live either on the beach, or at only a few fathoms' depth: Mr.

Reasons for studying the newer Groups first. Nomenclature of Formations. Detached Tertiary Formations scattered over Europe. Value of the Shell-bearing Mollusca in Classification. Classification of Tertiary Strata. Eocene, Miocene, and Pliocene Terms explained.

It is important to examine, in each of the cayos, on what this breccia reposes; whether it covers edifices of mollusca still living, or those secondary and tertiary rocks, which judging from the remains of coral they contain, seem to be the product of our days. The gypsum of the cayos opposite San Juan de los Remedios, on the northern coast of the island of Cuba, merits great attention.

There is, however, this singular circumstance, that when deposited on the under side of ledges of rock or in fissures, it appears always to be of a pale, pearly grey colour, even when of considerable thickness: hence one is led to suppose, that an abundance of light is necessary to the development of the dark colour, in the same manner as seems to be the case with the upper and exposed surfaces of the shells of living mollusca, which are always dark, compared with their under surfaces and with the parts habitually covered by the mantle of the animal.

Now this, it is evident, can be an appropriate definition only of the very lowest species, as of a Fungus or a Mollusca; and just as comprehensive an idea of the mystery of Life, as a Mollusca might give, can this definition afford. But this is not the only objection.