The localisation, both of genera and species, occurs all over the world. The genus _Achatinella_, which is peculiar to the Sandwich Islands, is found there in a profusion of species. It lives in the mountain valleys which radiate from the central ridge of each island, and each valley is characterised by its own peculiar set of species. The great carnivorous _Glandina_ is restricted to Central America and the adjacent parts of the two continents, with one or two species in Southern Europe. _Bulimus_ proper is restricted to South America; _Achatina_ to Africa south of the Sahara; _Tornatellina_ to the Pacific Islands; _Cochlostyla_ to the Philippines; _Cylindrella_ and _Bulimulus_ are peculiar to the New World; _Buliminus_, _Nanina_, _Scarabus_, and _Cassidula_ to the Old. Extreme cases of this restriction of habitat sometimes occur. Thus _Limnaea involuta_ is found only in a single small mountain tarn in Ireland; _Clausilia scalaris_ along a narrow strip of limestone in Malta; _Strophia nana_ is confined to a few square rods on an island that is itself a mere dot in the Caribbean Sea; the genus _Camptonyx_ occurs only in the neighbourhood of Mt. Girnar, in Gujerat; and _Lantzia_ in moss on the top of a mountain in Bourbon. Attempts to colonise snails in strange localities have usually resulted in failure, especially when the attempt has involved serious changes of environment. The common _Cochlicella acuta_ of our coasts resists all endeavours to establish it beyond a certain distance from the sea. Snails brought from the Riviera and placed under almost similar conditions of climate on our own southern coasts have lived for a while, but have very rarely taken permanent root. Mr. H. W. Kew[354] has collected a good many of these attempts to acclimatise species, the general success of which seems to depend almost entirely on a restoration of the old conditions of life.