304 



ISLAND LIFE. 



[part it. 



This difference is so remarkable that it is worth stating in a 

 comparative form : — 



Inoperculata. Operculata. Auricu'idse. 



Sandwich Islands 332 5 9 



Rest of Pacific Islands 200 115 16 



When we remember that in the West Indian Islands the 

 Operculata abound in a greater proportion than even in the 

 Pacific Islands generally, we are led to the conclusion that lime- 

 stone, which is plentiful in both these areas, is especially favour- 

 able to them, while the purely volcanic rocks are especially 

 unfavourable. The other peculiarities of the Sandwich Islands, 

 however, such as the enormous preponderance of the strictly 

 endemic Achatinellinae, and the presence of genera which occur 

 elsewhere only beyond the Pacific area in various parts of the 

 great continents, undoubtedly point to a very remote origin, at a 

 time when the distribution of many of the groups of mollusca 

 was very different from that which now prevails, 



A very interesting feature of the Sandwich group is the extent 

 to which the species and even the genera are confined to separate 

 islands. Thus the genera Carelia and Catinella with eight 

 species are peculiar to the island of Kaui; Bulimella, Apex, 

 Frickella, and Blauneria, to Oahu ; Perdicella to Maui ; and Ebur- 

 nella to Lanai. The Eev. John T. Gulick, who has made a 

 special study of the Achatinellinae, 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 



1 Journal of the Linnean Society^ 1873, p. 496. "On Diversity of 

 Evolution under one set of External Conditions." Proceedings of the 

 Zoological Society of London^ 1873, p. 80. "On the Classification of the 

 Achatinellidse." 



