ei INTRODUCTION. 
From a consideration of the land-shells collected on the Pacific 
islands, it seems possible to draw some fair inferences 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 indi- 
cations are equally strong that other groups had no such territorial 
connexion. 
The Samoa, Friendly, and Feejee Islands, are near to each other, 
and seem as if they must have intimate geological relations. 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 
eroups are more intimately related to the Society Islands, though at 
a much greater distance, than to the Feejee Islands. Not a single spe- 
cies of land-shell, found on the Feejees, was collected on either 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 Nanina. 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 Melania, 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 these islands have accidentally become more 
