12 Geograjpliical Distribution 



tration, I may mention, tliat the entire American continents, 

 from Greenland to Cape Horn, have afforded very few more 

 species than the West India Islands. 



Prof. C. B. Adams notices {Cvnt. to Conchology^ p. 213) 

 that if large groups of such islands as the West Indies should 

 be united in a common area of dry land, *' there would be 

 Zoological provinces containing five to tenfold as many species 

 as any which now exist." 



Darwin refers to the striking and important fact in regard 

 to the inhabitants of islands, that their affinity is " to those of 

 the nearest mainland without being actually the same species." 

 He instances the Gallapagos Archipelago, " where almost every 

 production of the land and water bears the unmistakable 

 stamp of the American Continent." This instance, as regards 

 land shells, is peculiarly appropriate. In the Gallapagos, Buli- 

 mus, the genus most largely developed in South America, is 

 alone represented. Dr. Hooker, in the Essay already referred 

 to, asserts "that most of those Australian orders and genera 

 which are found in other countries around Australia, have their 

 maximum development in Australia at points approximating 

 in geographical position towards those neighboring countries." 

 The generic affinity of the land shells of the West India Islands 

 to those of the adjacent parts of the American Continents is 

 certainly intimate, but the existence of several genera not 

 represented on the Continents shows other relationships — the 

 operation, it may be, of local causes. Seeing^ moreover, the 

 greater number of both genera and species, absolutely and 

 proportionately, in the islands under consideration, it may not 

 unreasonably be suggested that the insular stamp has rather 

 been impressed on the fauna of the adjacent continents, than 

 the reverse. 



Woodward {Manual^ p. 387) referring to the Madeiras, and 

 the problem of their colonization, observes — "There is evidence 

 that this mountain group has not arisen newly from the sea, 

 and great probability that it has become insulated by the sub- 



