264 HISTORY OF THE EUROPEAN FAUNA. 



merged since eocene times more than once. The 

 peculiar distribution of the genus might be explained, 

 I think, if we supposed the original home of Clausilia 

 to have been in Southern Asia, that from this centre 

 Southern Europe was colonised, where a new centre 

 developed in oligocene and miocene times, sending 

 colonies off to Madeira and across the old land- 

 connection which united Northern Africa and South 

 America about that time. The most active centre 

 of development then gradually shifted eastward 

 again, while the older centres were perhaps sub- 

 merged during the physical changes in the distri- 

 bution of land and water. 



I should have mentioned that the species 

 wandering westward and northward from this 

 South-European centre of distribution, would 

 naturally have joined the migrants which came 

 from beyond the borders of our continent. They 

 might thus appear to be true Oriental migrants, 

 and on a previous occasion I grouped all these 

 together under the term of "Southern Fauna," as 

 I assumed the observer to be stationed in the 

 British Islands. All new-comers from the south- 

 east, south, or south-west of Europe would be to 

 him southerners quite irrespective of their original 

 home, which might be in Southern Europe, Asia, 

 or Africa. 



The Swallow-tail is well known to all collectors 

 of Butterflies in England, though it has of late 

 years become very rare and is now confined to a 



