Palasontology . SS5 



" Iconographie" is to prove that such diflPerence has been 

 overlooked. He goes the length of saying, that, even when 

 species are, so far as the eye can judge, identical, they may 

 not be so. " Perhaps," he says, " there may exist species so 

 nearly allied, as to render it impossible to distinguish them ; 

 yet even that would not be to my eyes a proof of their iden- 

 tity ; it would only prove the insufficiency of our means of 

 observation :" and further, " the animals might differ though 

 the shells are alike." 



In the special part of his essay, M. Agassiz proceeds on 

 the position that the law of variation is not the same in all 

 classes, families, and genera ; iind selects his examples from 

 certain genera of Acephalous Mollusca in which the charac- 

 ters are very constant, viz. Artemis, VenuSi Cytherea, Cyprina, 

 and Lucina, on thirty-one forms of which genera, considered 

 by him as distinct species, he gives full comments and valu- 

 able details. One species only among them, the Cyprina 

 islandictty he admits to be at the same time recent and fossil. 



M. Agassiz introduces the same doctrine in his Monograph 

 of the Fishes of the Old Red Sandstone. Thus he says, at 

 page xi., that the characteristic fossils of each well-marked 

 geological epoch are the representatives of so many distinct 

 creations, and affirms that he has demonstrated " pour un 

 nombre assez considerable d^especes^'^ that the presumed iden- 

 tifications are exaggerated approximations of species resem- 

 bling one another, but neveHheless specifically distinct. 



"Whether species of Mollusca hitherto deemed common to 

 two or more of the tertiary periods be really, as M. Agassiz 

 affirms, distinct, is a doctrine that must await the concurrence 

 of experienced conchologists before it can be made the means 

 of overthrowing present generalizations, and the basis of new 

 ones. With regard to the Mammalia, certain eocene forms 

 have been repeatedly recognised in miocene strata, and the 

 continental miocene Mastodon has been satisfactorily deter- 

 mined as a fossil of our older pliocene (Norwich Crag). But 

 M. Agassiz is peculiarly unfortunate in citing Dr Falconer 

 and Major Cautley (p. xi.) as supporting, by their discoveries 

 of fossil animals in the Sub-Himalayan Mountains, his views 

 as to marked distinctions of the tertiary fauna, since they 



