PHILIPPI S COMPARATIVE TABLES OF MOLLUSCA. 7 



Of the species common to the tertiary period and the present 

 time, there are thus only 20 which do not inhabit that part of the 

 Mediterranean which washes the coast of South Italy ; and we may 

 hence already conclude with some confidence that the climate at the 

 period in question could not have been very different from what it 

 is now. 



But we have yet to consider the case of the 193 extinct species, 

 since it is possible that these may either, on the one hand, indicate 

 an arctic climate, corresponding with that assumed by the glacial 

 theorists, or, on the other hand, they may have required a still 

 warmer climate than we now find. It needs, however, merely a 

 glance at the foregoing list to show that neither of these cases can 

 be the true one. 



The species Aspergillum maniculatum, Perna Soldanii, Plicatula 

 mytilinay Strombus coronatus, Terebra fusca, T. duplicata, Voluta 

 rarispina, Ancillaria obsoleta, will be especially and immediately 

 recognised as indicating a warmer climate, since no species of any 

 of these genera occur in the temperate zone of the northern hemi- 

 sphere; and there is no doubt that Cytherea lamellosa has its nearest 

 analogue in C. cygnus^ whose habitat is in the neighbourhood of 

 Canton, and not, as Deshayes has imagined, in the Mediterranean. 



But, again, the number both of existing and extinct species that 

 seem to point to a warmer climate is very inconsiderable compared 

 with the whole number of species, and is counterbalanced by an- 

 other group, such as Mya truncata, Cyprina islandica, Fusus con- 

 trarius, &c., confined at present to the colder seas ; so that we may 

 fairly assume as an incontrovertible fact, that during the tertiary 

 period in South Italy the climate was neither much warmer nor much 

 colder than it is at present. And it cannot be considered as a serious 

 objection to this conclusion, that elephants, rhinoceroses and hippo- 

 potamuses have inhabited Sicily either during, or more recently than 

 the tertiary period, since species of these animals, distinct from 

 those which are now met with in warmer latitudes, might well exist 

 in the present climate of Sicily. We shall see presently that the 

 palaeontological relations do not allow us to admit of any demarca- 

 tion between the tertiary period and the periods of the diluvium 

 and alluvium. 



3. Differences with regard to species common to both periods. 



If, in the next place, we consider the relative abundance of dif- 

 ferent species, in which the physiognomy, so to speak, of the mol- 

 luscous fauna consists, we find that several species were equally 

 common in the existing seas and during the tertiary period, but that 

 a considerable number which were formerly very abundant are now 

 rare, or have actually become extinct, while, on the other hand, many 

 which were then rare, or had not been introduced, are now connnon. 

 In the following lists, the species printed in italics belong to the 

 former group, — that which includes those once abundant, but now 

 extinct. 



