Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/226

 222 Genera of this family abound among living fishes; but they have not been found fossil in any stratum older than the Lias; they occur also in the Jurassic limestone.

Throughout the tertiary formation they are very abundant; of one genus, Myliobates, there are seven known species; from these have been derived the palates that are so frequent in the London clay and crag. (See Pl. 27d, B. Fig. 14.) The genus Trygon, and Torpedo, occur also in the Tertiary formations.

In the facts before us, we have an uninterrupted series of evidence, derived from the family of Fishes, by which both bony and cartilaginous forms of this family, are shown to have prevailed during every period, from the first commencement of submarine life, unto the present hour. The similarity of the teeth, and scales, and bones, of the earliest Sauroid Fishes of the coal formation (Megalichthys), to those of the living Lepidosteus, and the correspondence of the teeth and bony spines of the only living Cestruciont in the family of Sharks, with the numerous extinct forms of that sub-family, which abound throughout the Carboniferous and Secondary formations, connect extreme points of this grand vertebrated division of the animal kingdom, by one unbroken chain, more uniform and continuous than has hitherto been discovered in the entire range of geological researches.

It results from the review here taken of the history of fossil Fishes, that this important class of vertebrated animals presented its actual gradations of structure amongst the earliest inhabitants of our planet; and has ever performed the same important functions in the general economy of nature, as those discharged by their living representatives in our modern seas, and lakes, and rivers. The great purpose of their existence seems at all times to have been, to