EVIDENCE OF FOSSIL REMAINS 103 



stragglers from the mainland. The first settlers in 

 one place would send out colonies to others, where 

 independent evolution would result in the appearance 

 of minor differences peculiar to the single island. 

 In this manner science interprets the general agree- 

 ment between the animals of the Azores Islands and 

 the fauna of the northwestern part of Africa, the 

 nearest body of land, from which it would be most 

 natural for the ancestors of the island fauna to come. 

 The land-snails inhabiting the various groups of 

 islands scattered throughout the vast extent of the 

 Pacific Ocean provide the richest and most ideal material 

 for the demonstration of the principles of geographical 

 distribution. In the Hawaiian Islands snails of the 

 family of Achatinellida3 occur in great abundance, 

 and like the lizards of the Galapagos Islands different 

 species occur on the different members of the group. 

 Within the confines of one and the same island, they 

 vary from valley to valley, and the correlation between 

 their isolation in geographical respects and specific dif- 

 ferences on the other hand, first pointed out by Gulick, 

 makes this tribe of 'animals classical material. In 

 Polynesia and Melanesia are found close relatives of 

 the Achatinellidae, namely, the Partulae, which are 

 thus in relative proximity to the Achatinellidse and 

 not on the other side of the world. Furthermore, 

 the Partulse are not alike in all of the groups of Polynesia 

 where they occur; the species of the Society Islands 

 are absolutely distinct from those of the Marquesas, 

 Tonga, Samoan, and Solomon Islands, although they 

 agree closely in the basic characters that justify their 

 reference to a single genus. The geological evidence 



