LAJfD HEGIOJTS. 87 



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 conti- 

 nents, but on the islands, till every little rock in the ocean haa 

 its peculiar inhabitants — the survivors, seem.ingly, 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 many geographical subdivisions.* Amongst 

 the land- snails are several species to which a nearly World-wide 

 range has been assigned, sometimes erroneously, as when Helix 

 cicatricosa is a,ttributed to Senegal and China, or Helix similaria 

 Per. to Brazil and India ; and often correctly, but only because 

 they have been carried to distant localities by human agency. 

 Land-snails are in favour with Portuguese sailors, as ' ' live sea 

 stock; " and they have naturalised the common garden-snail of 

 Europe {Helix aspersa) in Algeria, the Azores, and Brazil ; and 

 Helix lactea at Teneriffe and Mte. Video. Achatina fidica has 

 been taken from Afirica to the Mauritius, and thence to Calcutta, 

 where it has been established by a living naturalist ; and Helix 

 hortensis has been carried from the old country to America, and 

 naturalised on the coast of New England and the banks of the 

 St. Lawrence. Bulimus Goodalli, indigenous to the West Indies 

 and S. America, has been introduced into English pineries and 

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

 moss and decayed leaves, inhabits Europe, the Caucasus, 

 Madeira, the Cape (introduced), and N. America as far as the 

 Missouri. Helix cellaria inhabits Europe and the Northern 

 States of America, and has been carried abroad with the roots 

 of plants, or attached to water-casks, and naturalised at the 

 Cape and New Zealand. Testacella maugei has been transported 

 from the Canary Islands to England. 



The fresh-water Pulmonifera — Limncea, PJiysa, Planorhis, 

 Ancylus — and the amphibious Succinea, have a nearly world- 

 wide range ; and like aquatic plants and insects, often re-appear, 

 even at the antipodes, under familiar forms. The range of the 

 gill-breathing fresh-water shells is more restricted. 



The Old World and America may be regarded as provinces of 

 paramount importance, having no species in common (except a 



* In cataloguing Unio7iidce, the river and country of eacli species shotild be stated. 

 American authors are too often contented with recording such localities as "Nash- 

 ville '' and " Smithville," which are quite unintelligible. Almost as uncertain in their 

 meaning are S. Vincent, S. Cruz, S. Thomas. Prince's Id. ; whilst the latinised names 

 of places often defy all attempts at re-translation. 



