222 GENERAL CONCLUSION. 



dians. 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 abun- 

 dant ; of one genus, Myliobates, there are seven known spe- 

 cies ; from these have been derived the palates that are so 

 frequent in the London clay and crag. (See PI. 21^, B. Fig. 

 14.) The genus Trygon, and Torpedo, occur also in the 

 Tertiary formations. 



Conclusion. 



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 com- 

 mencement of submarine life, unto the present hour. The 

 similiarity 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 

 tlie teeth and bony spines of the only living Cestraciont 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 pur- 

 pose of their existence seems at all times to have been, to 



