300 Professor Agassiz on 



the fact (the importance of which can be properly appreciated 

 only by a zoologist), that along with the very diversified types 

 which succeed one another in the series of formations, there 

 are others not less ancient, which resemble, in a surprising de- 

 gree, those of the present creation. M. Pictet shews himself 

 to be equally competent to draw just conclusions from all these 

 facts, and thus to present incontestible proofs in opposition to 

 the idea of the transition of species. For my own part, I can- 

 not doubt but that zoologists, by basing their opinions on ana- 

 tomy and physiology, will soon entirely annihilate the vain 

 theory of the derivation of existing beings from a small num- 

 ber of primitive types ; but I think that M. Pictet deceives 

 himself, when he sees, in the whole facts relative to the his- 

 tory of fossil reptiles, a complete demonstration of the dif- 

 ference between the living and the tertiary species. We still 

 know too little of tertiary reptiles, to justify us completely in 

 drawing such a conclusion ; although, I again repeat, that I am 

 myself convinced of the truth of that assertion. The endea- 

 vours of M. Pictet to group in a natural manner so many ex- 

 tinct genera of reptiles, which are often very imperfectly 

 known, seem to me to merit the approval of naturalists ; and 

 his family of Dinosaurians will undoubtedly be adopted. As 

 I do not wish to enter into greater details regarding this class 

 than respecting the Mammifera, I shall here limit my obser- 

 vations to some critical details, which rather aff'ect the inves- 

 tigations quoted from others, than our author himself. Thus 

 the remains of the Trionyx, which M. Kutorga assigns to the 

 sandstone of the neighbourhood of Dorpat, are in fact bones 

 of fishes of the genus Asterolepis, which I had described un- 

 der the name of Chelonichthys, before I was aware that they 

 had already received an admissible appellation. 



With regard to the genus Saurocephalus of Harlan, Avhich 

 that author includes among the reptiles, M. Pictet has com- 

 mitted a mistake, which it is only necessary to point out in 

 order to rectify. 1 he animal is twice described in his book : 

 first of all, and erroneously, among the reptiles ; and afterwards 

 in its proper place among the fishes, in the family of the 

 Sphyrendides, where I had arranged it. 



We now come to the class of fishes. As my own researches 

 regarding these fossils have been the principal basis of this 



