It appears unquestionable that marine genera from high northern latitudes are provided with shells of uniform colour, or whitish with a pale brown epidermis; spots, bands, or stripes seldom occur. The arctic forms of _Buccinum_, _Trophon_, _Chrysodomus_, _Margarita_, _Crenella_, _Leda_, _Yoldia_, _Astarte_ illustrate this fact. In the more temperate seas of Europe, colours tend on the whole to increase, although there are certain genera (_e.g._ _Pecten_) which are not more brightly coloured in Mediterranean than in Icelandic waters. Land Mollusca inhabiting the mainland of a continent not unfrequently become smaller when they have spread to adjacent islands where perhaps the rainfall is less abundant or the soil and food-supply less nicely adjusted to their wants. _Orthalicus undatus_ is decidedly larger on the mainland of S. America than on the adjacent islands of Trinidad and Grenada. Specimens of _Bulimulus exilis_ from Barbados are invariably broader and more obese than those from S. Thomas, while those from the volcanic island of S. Lucia, where lime is deficient, are small and very slender. _Streptaxis deformis_, as occurring at Trinidad, is only half the size of specimens from Georgetown, Demerara.[189] Certain localities appear, for some unexplained reason, to be particularly favourable to the production of albino varieties. The neighbourhood of Lewes, in Sussex, has produced no fewer than fourteen of these forms of land Mollusca and five of fresh-water.[190] Our common _Helix aspersa_, as found near Bristol, is said to be ‘dark coloured’; about Western-super-mare ‘brown, with black markings’; near Bath ‘very pale and much mottled’; at Cheddar ‘very solid and large.’[191] Sometimes the same kind of variation is exhibited by different species in the same locality. Thus specimens of _H. aspersa_, _H. nemoralis_, and _H. hortensis_, taken from the same bank at Torquay, presented a straw-coloured tinge of ground colour, with red-brown bands or markings. Trochiform _H. nemoralis_ and _H. arbustorum_, sinistral _H. hortensis_ and _H. aspersa_, sinistral _H. aspersa_ and _H. virgata_, and similarly banded forms of _H. caperata_ and _H. virgata_, have been taken together.[192]