Remarks on Mollusca and Shells. 79 



as to the relations of the lands which once occupied the area 

 of the Pacific Ocean, and whose mountain peaks evidently 

 now indicate, or constitute, the islands with which it is now 

 studded. By observation of the species, we think there are 

 strong indications that some groups of islands have an inti- 

 mate relation to each other, and belonged at least, to the peaks 

 of the same mountain ranges, before they were submerged, 

 while the indications are equally strong, that other groups 

 had no such territorial connection. 



The Samoa, Friendly, and Feejee Islands are near to each 

 other, and seem as if they must have intimate geological re- 

 lations. The Samoa and Friendly Islands give evidence of 

 such relation, the same forms and many of the same species 

 occurring on both groups. But, if we may draw inferences 

 from the land-shells, these two groups are more intimately 

 related to the Society Islands, though at a much greater dis- 

 tance, than to the Feejee Islands. Not a single species of land- 

 shell found on the Feejees was collected on either side of the 

 other groups. Several genera which are common to the 

 other groups are wanting in the Feejees. Thus, no specimen 

 of Succinea or Partula, genera so abundant in the Society 

 and Samoa Islands, was found at the Feejees ; and the true 

 Helix, especially the pyramidal forms, so remarkable in the 

 other groups, seemed to be replaced by large species of 

 Nomina. On the other hand, large and peculiar species of 

 Bulimus occur abundantly on the Feejees, while nothing of the 

 kind occurs on any of the other islands. Indeed, judging from 

 the land-shells, the Feejees are more nearly allied to the 

 islands to the westward, such as the New Hebrides, than to 

 the Friendly Islands on the east, though so much nearer. 

 When we examine the fluviatile shells, however, we do not 

 find the same distinction. Many of the same species of Mela- 

 nia, Navicella, and Neritina, seem to occur in all the groups, 

 though the large coronated species of Melania prevail in the 

 Feejees. There is some reason to suspect, moreover, that 

 the fresh-water shells collected at those islands have acci- 

 dentally become more or less mingled. It must also be con- 

 sidered that the Navicella, and more especially Neritina, is 

 oftentimes decidedly littoral, and even marine, in its habits. 



