LAND REGIONS. 179 



genera of terrestrial mollnsca; Cuba, Jamaica, Haj^ti, Madagascar, 

 New Caledonia, Australia, the Philippines, etc., may be cited. 

 Even small islands, such as Malta, Lampedusa, Cos, Naxos, 

 Corfu, Zante, Lesbos, Eub?ea, Rhodes, in the Mediterranean Sea, 

 are characterized by the presence of species not found elsewhere. 

 The exceptions are, as in the case of England, where the present 

 species, identical with those of the adjacent continent, antedate 

 the formation of the British Channel. 



It has been often remarked that the northern part of the map 

 of the world presents the appearance of vastly-extended, conti- 

 nental plains, much of which is, geologically speaking, new 

 land. In the southern hemisphere the continents taper off into 

 promontories and peninsulas, or have long since broken up into 

 islands. Connected with this is the remarkable fact that only 

 around the shores of the Arctic Sea are the same animals and 

 plants found through every meridian ; and that in passing south- 

 ward, along the three principal lines of land, specific identities 

 give way to mere identity of genera ; these are replaced by 

 family resemblances, and at last even the families of animals and 

 plants become in great measure distinct, not only on the great 

 continents, but on the islands, till every little rock in the ocean 

 has its peculiar inhabitants — the survivors, seemingly, of tribes 

 which the sea has swallowed up (Waterhouse). 



The two largest genera, or principal types of the land and 

 fresh-water shells. Helix and Unio, have an almost universal 

 range, but admit of man^^ geographical subdivisions. Amongst 

 the land snails are sevei'al species to which a nearl}^ world-wide 

 range has been assigned, sometimes erroneouslj^, and often 

 correctly, but usually only because they have been carried to 

 distant localities by human agency. Land snails are in favor 

 with Portuguese sailors, as "live sea stock;" and they have 

 naturalized the common garden-snail of Europe {Helix aspersa) 

 in Algeria, the Azores, and Brazil;* and Helix lactea at Teneriffe' 

 and Montevideo. Achatina fulica has been taken from Africa 

 to the Mauritius, and thence to Calcutta, where it has been 

 established by a living naturalist ; and Helix horlensis has been 

 carried from the old country to America, and naturalized on the 

 coast of New England and the banks of the St. Lawrence, and 

 elsewhere. Buliinus Goodalli, indigenous to the West Indies and 

 South America, has been introduced into English pineries and 

 to Mauritius. Helix pulchella, one of the small species found in 

 moss and decayed leaves, inhabits Europe, the Caucasus, Madeira, 



* French emigrants introduced this species twenty-three years ago at 

 San .Tose, California, where it still exists, within a limited area, and is 

 gathered for food. 



