284 



REGIONS OF DISTRIBUTION 



CHAP. 



the Palaearctic, Oriental, Australasian, Ethiopian, Nearctic, and 

 Neotropical. To these is sometimes added a seventh, the Neant- 

 arctic, consisting of Chili and Patagonia (and certain islands of 

 the south Atlantic) ; but since the Mollusca of Chili unmis- 

 takably form a part of the Neotropical fauna, it seems hardly 

 worth while to recognise a separate region for those of the 

 extreme south of South America, which have no peculiar char- 

 acteristics. 



In certain points the exact limits of these regions, as indi- 

 cated by the Mollusca, will probably not correspond to those 

 which are marked out by other zoological classes. Wallace's 

 line, for instance, does not exist, as far as the Mollusca are 

 concerned. 



These regions may be further subdivided into sub-regions, 

 thus : — 



Kesrions 



Palaearctic 



Oriental 



Sub-regions 



[" Septentrional 

 ^ Mediterranean 

 [ Central Asiatic 

 [ Indo-Malay 

 [ Chinese 



Nearctic 



[ Papuan 

 Australasian j Australian 

 [ Polynesian 



Kegions Sub-regions 



r Central African 

 Ethiopian -j South African 



[ iSIalagasy 



r American 



[ Calif or nian 



1 Antillean 



I Central American 

 Neotropical i Colombian 



j Brazilian 



[ Chilian 



A. The Palaearctic Region 



The southern boundary of this region is the northern limit of 

 the African Sahara, the Mediterranean forming no break what- 

 ever in its continuity. In Asia this boundary is less well 

 marked, but roughly corresponds to the southernmost of the vast 

 ranges of mountains which border the great tablelands of central 

 Asia. Across Africa the line of desert is well defined ; but in 

 the north-east, as the desert approaches more nearly to the sea, 

 the African extent of the region is correspondingly narrowed 

 until it becomes little more than a strip of coast land, scarcely 

 widening even in Lower Egj^pt. On the Morocco coast, Palae- 

 arctic land forms penetrate as far south as Cape Nun.^ At 

 its eastern extremity the line becomes less well defined, but 

 1 Morelet, Journal de Conch. 1875, p. 194. 



