PROOFS, ILLUSTRATIONS, AUTHORITIES, ETC. xi 



fish, the Cephalaspides, that family which recedes most from the 

 ordinary form of other fishes, are of least duration, being confined to 

 the Old Red Sandstone ; the Acanthodians are next in this respect, 

 coming down no later than the coal formation. 



Yet " the different genera of the Cephalaspides already show a 

 gradation, although faintly marked, in their conformation becoming 

 more and more perfect. It is thus tbat, on the one hand, the winged 

 appendages of the Pterichthys and Pamphractus are lost in the Coo- 

 costei and Cephalaspis, where the} 7 are replaced by ordinary fins; 

 while, on the other hand, there is an evident approximation between 

 the Coccostei and the broadly cuirassed genera of the family of 

 Celacanthes, such as Asterolepis and Bothriolepis. The thick and 

 short form of the Pterichthys and the very incomplete development 

 of their fins, evidently show that they were fishes of little agility, 

 living in shoals in mud, moving sluggishly, and destined to become 

 the prey of others. Among the Cephalaspides [genus of this name] 

 the broad shield with which they are covered, and their eyes situated 

 on the upper side, indicate the same mode of life ; but in them the 

 trunk becomes more moveable, and the tail,, the most powerful in- 

 strument of motion, is furnished with fins, and becomes fit to 

 execute the most rapid motions. The Coccostei finally, were evi- 

 dently, even at this step in the gradation, voracious "fishes, as is 

 shown by their conical sharp teeth, and their long flat and flexible 

 tail." 



The gradation is -even indicated as going on to the family of Cela- 

 canthes. " There is no doubt," pursues M. Agassiz, " a wide in- 

 terval between this and the formidable armature of the Bothriolepis 

 and the needle-like teeth of Dendrodes (Asterolepis) : but it will be 

 -admitted that there is an advance towards the rapacious character in 

 the family of Cephalaspides, and if we join to this the structure of the 

 plates, the resemblance of the granulated scattered points of the 

 Coccostei to the asterisks of the plates of asterolepis, we shall soon 

 be convinced that it is not necessary to take a long step to advance 

 from the Coccostei to the cuirassed Celacanthes." 



8. IN ALL THE ORDERS OF ANCIENT ANIMALS, THERE 

 IS AN ASCENDING GRADATION OF CHARACTER 

 FROM FIRST TO LAST. 



" The agreement between the zoological affinities and the geolo- 

 gical division of types in the series of formations is so striking, 

 especially in certain classes which have of late been the object of 

 particular study, that I think it may now be laid down as a fact, that 

 systematic classifications which are not, at the same time, the expres- 

 sion of the succession of families in the order of time, can no longer 

 be considered as expressing the real affinities existing among the 



