156 MARINE PROVINCES. 



The following have been thought peculiar to the warmer 

 regions of the sea : 



Nautilus, Conus, Coluinbella, Perna, 



Rostellaria, Harpa, Cyprsea, Vulsella, 



Triton, Oliva, , Nerita, Tridacna, 



Cancellaria, Voluta, Spondylus, Crassatella, 



Terebra, Marginella, Plicatula, Sanguinolaria. 



But it must not be inferred that these genera had always their 

 present distribution. On the contrary, nearly the whole of them 

 have existed in the British and American seas at no very remote 

 geological period. Rhynchonella and Astarte were formerly 

 " tropical shells ; " and since the period of the English chalk- 

 formation there have been living Nautili in the North Sea, and 

 Cones and Olives in the " London basin." 



The tropical and subtropical provinces might be naturally 

 grouped in three principal divisions, viz., the Atlantic, the Indo- 

 Paciflc, and the West American — divisions which are bounded 

 by meridians of longitude, not by parallels of latitude. The 

 Arctic province is comparatively small and exceptional ; and 

 the three most southern Faunas of America, Africa, and Australia 

 differ extremely, but not on account of climate. 



If only a small extent of sea-coast is examined, the character 

 of its mollusca will be found to depend very much upon the 

 nature of the shore, the tides, depth, and local circumstances ; 

 but these peculiarities will disappear when the survey is extended 

 to a region sufficiently large to include every ordinary variety 

 of condition. 



It has been stated that each fauna consists of a number of pecu- 

 liar species, properly, more than half; and of a smaller number 

 which are common to some other provinces. By ascertaining 

 the direction of the tides and currents, and the circumstances 

 under which the species occur, it may be possible to determine to 

 which province these more widely diffused mollusca originally 

 belonged. And when species occur both recent and fossil it is 

 easy to perceive the direction in which their migrations have 

 taken place. The fauna of the Mediterranean has been critically 

 examined by Prof Forbes and M. Philippi, with this result — ' 

 that a large proportion of its population has migrated into it 

 from the Atlantic, and a smaller number from the Red Sea, and 

 that the supposed peculiar species are diminishing so rapidly 

 with every new research in the Atlantic, that it can no longer 

 rank as a province distinct from the Lusitanian. 



MARINE PROVINCES. 



There are eighteen Marine Provinces : 



1, Arctic; 2, Boreal; 3, Celtic; 4, Lusitanian; 5, Aralo- 

 Caspian ; 6, West African ; 1, South African ; 8, Indo-Pacific ; 



