PRELIMINARY CONSIDERATIONS. 49 



which is generally known by the name of " Atlantis." 

 From this a branch went westward to the New 

 World and another eastward as far as Southern Asia, 

 but Arion and a number of other genera are more or 

 less confined to South-Western Europe. Only a few 

 species of Anon have a wide range in Europe, one of 

 them, A. subfuscus, crossing the borders of our con- 

 tinent into Siberia. In the British Islands and in 

 Western Germany, which are about equi-distant from 

 the supposed creative centre of the genus, there are 

 found five species. In France six or seven species 

 are met with, and in Spain and Portugal about ten. 

 Towards the east, Arions diminish in number. This 

 genus, therefore, forms part of a migration which I 

 have designated as " Lusitanian " from Lusitania, 

 the name applied by the Romans to what we 

 now call Portugal. Another genus of slugs, Geo- 

 malacuS) is interesting from the fact that one species 

 occurs in the British Islands, being otherwise con- 

 fined to the Lusitanian province. Parmacella, a slug- 

 like animal bearing a tiny shell at the extremity of its 

 tail, has probably likewise had its origin in this part of 

 Europe. All this, however, will be more fully referred 

 to in the seventh chapter, which deals with the 

 Lusitanian fauna. 



As regards the Alpine centre of origin, Dr. Kobelt 

 considers three groups of mollusca as especially 

 characteristic of the Alps, viz., the sub -genus Carnpylaea 

 of the great and widely-spread genus Helix, and the 

 genera Pomatias and Zonites. The latter, which is not 



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