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The task of arranging all this disorder has at length been undertaken by an individual, to whose hands Cuvier at once consigned the materials he had himself collected for this important work. The able researches of Professor Agassiz have already extended the number of fossil Fishes to two hundred genera, and more than eight hundred and fifty species. The results, of his inquiry throw a new and most important light on the state of the earth, during each of the great periods into which its past history has been divided. The study of fossil Ichthyology is therefore of peculiar importance to the geologist, as it enables him to follow an entire Class of animals, of so high a Division as the vertebrate, through the whole series of geological formations; and to institute comparisons between their various conditions during successive Periods of the earth's formation, such as Cuvier could carry only to a much more limited extent in the classes of Reptiles, Birds, and Mammifers, for want of adequate materials.

The system upon which M. Agassiz has established his classification of recent Fishes is in a peculiar degree applicable to fossil Fishes, being founded on the character of the external coverings, or Scales. This character is so sure and constant, that the preservation of a single scale, will often announce the genus and even the species of the animal from which it was derived; just as certain feathers announce to a skilful ornithologist the genus or species of a Bird. It follows still further, that as the nature of their outward covering indicates the relations of all animals to the external world, we derive from their scales certain indications of the

Cuvier; and one great proof of this imperfection is that they have led to no general results, either in Natural History, Physiology, or Geology.