317 ISLAND LIFE 



genus of geckoes, but both its locality and affinities appear 

 to be somewhat doubtful. 



Land- shells — The only other group of animals which 

 has been carefully studied, and which presents features of 

 especial interest, are the land and freshwater shells. 

 These are very numerous, about thirty-five genera, and 

 nearly five hundred species having been described ; and 

 it is remarkable that this single archipelago contains as 

 many species of these molluscs as all the other Polynesian 

 Islands from the Pelew Islands and Samoa to the 

 Marquesas. Almost all the species are peculiar, and more 

 than three-fourths of the whole belong to peculiar genera, 

 nine of which constitute the family Achatinellidse, almost 

 confined to this group of islands and constituting its most 

 distinguishing feature.^ Only nine species are found in 

 other parts of the world, and several of these (possibly 

 all) are recent introductions. 



The Rev. John T. Gulick, who has made a special study 

 of the Achatinellidse, informs us that the average range of 

 the species in this sub-family is five or six miles, while 

 some are restricted to but one or two square miles, and 

 only very few have the range of a whole island. Each valley, 

 and often each side of a valley, and sometimes even every 

 ridge and peak possesses its peculiar species.^ The island 

 of Oahu, in which the capital is situated, has furnished 

 about half the species already known. This is partly due 

 to its being more forest-clad, but also, no doubt, in part to 

 its being better explored, so that notwithstanding the 

 exceptional riches of the group, we have no reason to 

 suppose that there are not many more species to be found 

 in the less explored islands. Mr. Gulick tells us that the 

 forest region that covers one of the mountain ranges of 

 Oahu is about forty miles in length, and five or six miles 

 in width, yet this small territory furnishes about 175 



^ The genus Partula of the South Pacific Islands is sometimes classed 

 with the Achatinellidse, but this is not considered certain. 



2 Journal of the Linnean Society, 1873, p. 496. **0n Diversity of 

 Evolution under one set of External Ck)nditions." Proceedings of the 

 Zoological Society of London, 1873, p. 80. **0n the Classification of the 

 Achatinellidse. " 



