122 HISTORY OF THE EUROPEAN FAUNA. 



species belong to a younger or newer section of our 

 fauna than the local ones. In many cases this may 

 be quite true, but we possess also a large number of 

 common and widely-spread forms which bear the 

 impress of antiquity upon them. We have the most 

 positive proof of the antiquity of the very common 

 small circular Snail (Helix: rotundata}, since it was 

 found in miocene freshwater deposits near Bor- 

 deaux. Many other examples might be mentioned 

 to show that, though discontinuous range is generally 

 a proof of antiquity, continuous range is not always a 

 sign of the opposite. Some species, in fact, appear to 

 be short-lived and disinclined to spread, whilst others 

 multiply rapidly even under a change of temperature 

 and climate, and are to be found almost everywhere. 

 But even if we supposed, with Mr. Carpenter, that 

 these widely-ranging species must have been confined 

 during the Glacial period to the more southern parts 

 of England, the idea that they afterwards made their 

 way northwards along the eastern shore of the Irish 

 Sea and then passed into Ireland, does not appeal to 

 me. Southern England was occupied at that very 

 same time by an assemblage of Siberian mammals. 

 Mr. Carpenter thinks these might have been kept 

 out of Ireland by an arm of the sea until the land- 

 connection with North-western England had broken 

 down. But if an arm of the sea could keep out the 

 Siberian mammals it would also keep out the widely- 

 spread British species of the general fauna. On the 

 other hand, I quite admit that my view of the survival 



