CHAPTER V. 



PART II. 

 FOSSIL FISHES OF THE GANOID ORDER. 



ICHTHYOLITES, OR FOSSIL FISHES AGASSIz's CLASSIFICATION FINS OP 



FISHES TEETH OF FISHES TAILS OF FISHES GANOID ORDER CEPHA- 



LASPIDIANS LEPIDOIDS ACANTHODIANS DIPTERIANS SAUROIDS CELA- 



CANTHS SCLERODERMS PYCNODONS. 



ICHTHYOLITES, OR FOSSIL FISHES. The fossil remains of 

 FISHES are of great importance in a geological point of view, 

 for they demonstrate the existence of highly organized beings 

 in the most ancient fossiliferous strata, and the continuance 

 of the same Class of vertebrata, variously modified, through 

 the entire series of subsequent deposits to the present time. 

 Each formation contains certain groups of fishes, distin- 

 guished by well-marked peculiarities of structure. Thus, 

 according to the data at present obtained, all the osseous 

 fishes that lived antecedently to the Chalk, belong to genera 

 which have no representatives in the existing ichthyic faunas, 

 and were covered by enamelled rhomboidal scales. 



The state of preservation in which the fossil remains of 

 fishes occur, has resulted from the relative delicacy or dura- 

 bility of the original structures, and on the chemical nature 

 and mechanical conditions of the deposits in which they were 

 imbedded. Thus the Ichthyolites of the most ancient sedi- 

 mentary strata, the Silurian and Devonian, which are cha- 

 racterized by their dense integument and enamelled scales, 

 often present the entire forms of the originals, and generally 

 retain considerable portions of the scales connected, with the 

 fins, and other appendages; while those of later formations, 

 being chiefly species with delicate scales, more frequently 



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