THE SANDWICH ISLAXDS 317 



land-shells as all the other Polynesian Islands from the 

 Pelew Islands and Samoa to the Marquesas. All the 

 species are peculiar, and about three-fourths of the whole 

 belong to peculiar genera, fourteen of which constitute the 

 subfamily Achatinellinse, entirely confined to this group of 

 islands and constituting its most distinguishing feature. 

 Thirteen genera (comprising sixty-four species) are found 

 also in the other Polynesian Islands, but three genera of 

 Auriculidte (Plecotrema, Pedipes, and Blauneria) are not 

 found in the Pacific, but inhabit — the former genus 

 Australia, China, Bourbon, and Cuba, the two latter the 

 West Indian Islands. Another remarkable peculiarity of 

 these islands is the small number of Operculata, which are 

 represented by only one genus and five species, while the 

 other Pacific Islands have twenty genera and 115 species, 

 or more than half the number of the Inoperculata. This 

 difference is so remarkable that it is worth stating in a 

 comparative form : — 



Inoperculata Operculata. Auriculidse. 



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 projDortion than even 

 in the Pacific Islands generally, we are led to the con- 

 clusion that limestone, which is plentiful in both these 

 areas, is especially favourable 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 Achati- 

 nellinse, 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 novr 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 Eburnella to Lanai. 



