214 Mr. J. W. Kirkby on the Recurrence 



differentiation of essential anatomical details, and of the more 

 fragile characters, is usually accompanied by differences in those 

 characters which survive fossilization. It is very rarely indeed 

 that a shell is only known to be distinct on account of some 

 anatomical peculiarity. I am therefore not disposed to think, as 

 Prof. King seems to fear, that palaeontologists will often arrive 

 at erroneous conclusions in respect to species from their inability 

 to employ all the means that are at the disposal of naturalists. 

 And this opinion is borne out by what we know of such species 

 as occur both fossil and recent. Take those of the Crag, for 

 instance, or of any later Tertiary deposit, and it will be found 

 that absence of colour, epidermis, opalescence, and of all anato- 

 mical details has not seriously interfered with their being pro- 

 perly discriminated. There seems, in my opinion, more reason 

 to fear the creation of too many species by palaeontologists than 

 that any considerable number will be overlooked by them ; for 

 it should be remembered that there is a tendency in fossilization 

 to produce differences where none exist, as well as to obliterate 

 others that really characterize species. Fossils of one species 

 preserved as casts, or in a semi-testiferous state, or with the 

 shell in good condition, present very different appearances, and 

 repeatedly lead to false determinations. And the fragmentary 

 state in which some fossils occur, their being viewed in different 

 aspects, and the various alterations effected by pressure and other 

 causes, all tend to the adoption of species that have no real 

 existence. 



However, Prof. King, to illustrate his own views in respect to 

 the influence that fossilization would have on recent shells, re- 

 marks that *^^ nearly every British species oi Mactra and Lito- 

 rina, if occurring as fossils in palaeozoic rocks, would have had 

 their independent creation ignored, and have been respectively 

 named Mactra multiformis and Litorina variabilis '' on our me- 

 thod of determining species. Now, though these genera contain 

 certain British species which could never have been confounded 

 even as palaeozoic fossils. Prof. King is assuredly aware that they 

 are two of the most difficult groups of British shells, and that 

 several of their reputed species are acknowledged to be mere 

 varieties by most naturalists. Had they, therefore, occurred in 

 palaeozoic or any other rocks, the careful palaeontologist would 

 certainly have put many of their forms together, just, in fact, as 

 the judicious conchologist does now. Thus the argument which 

 Prof. King wishes to derive from these examples is rendered in- 

 valid by this fact; for it is certainly not to be expected that 

 palaeontologists would be able to see specific differences after 

 fossililization, where naturalists for the most part denied their 

 existence before that process. 



