The existing species of animals scientifically determined by naturalists amount to upwards of one hundred thousand, while those known in a fossil state scarcely exceed twenty-five thousand; yet the latter comprise examples of all the classes, and most of the families and genera, which still inhabit our planet. Although our notice of these remains must necessarily be very general, we shall endeavour to describe all that are of peculiar interest, either in a geological or zoological point of view; or which from their prevalence, or wide distribution, will frequently be met with by the collector in the course of his researches.

Our examination will commence with animal organisms of the simplest structure, and proceed in an ascending order, in accordance with the usual zoological classifications; but, as in the botanical department, it will be convenient occasionally to include the consideration of the fossil remains of more than one family in the same section, when associated in a particular locality or deposit.

In the preliminary remarks on the nature of Organic Remains (ante, p. 43.), the various conditions in which the durable structures of animals are preserved in the mineral kingdom, were fully explained; we may therefore at once enter upon the investigation of this most important division of our subject; that to which the term PalÆontology, is, indeed, restricted by some authors.

The fossil remains of the animal kingdom will be treated of under the following heads:—