392 T. Bland on the Geographical Distribution of Mollusca. 
distribution of Animals.” ‘ Notwithstanding,” say the authors, 
“the uniform nature of the watery element, the animals which 
dwell in it are not dispersed at random; and though the limits 
of the marine may be less easily defined than those of terrestrial 
faunas,*still, marked differences between the animals of great 
basins are not less observable. Properly to apprehend how ma- 
rine animals may be distributed into local faunas, it must be 
remembered that their residence is not in the high sea, but along 
the coasts of continents, and on soundings.” : And far-+ 
ther,—‘“ A very influential cause in the distribution of aquatic 
animals is the depth of the water; so that several zoological 
zones, receding from the shore, may be defined, according to the 
depth of the water; much in the same manner as we mark dif- 
ferent zones at different elevations in ascending mountains. The 
Mollusks and even the fishes found near the shore in shallow 
water, differ, in general, from those living at the depth of twenty 
or thirty feet, and these again are found to be different from those 
which are met with at a greater depth.”—p. 192. 
In the various numbers of his “ Contributions to Conchology,” 
(No. 1, published in Sept., 1849, and No. 10, the last, in Nov., 
1851,) Professor Adams describes the curious local distribution 
of the terrestrial shells of Jamaica, and corrects many errors with 
regard to them. He found some species improperly attributed to 
Jamaica, and other species peculiar to that island, referred to other 
localities. It is now satisfactorily proved, that of the 357 species, the 
whole number of strictly terrestrial shells at present known to in- 
habit Jamaica, not more than 10 species are found in other islands. 
In “ Contributions” No. 4, Professor Adams remarks, “ With 
this extremely local distribution of the terrestrial Mollusca in the 
West Indies may be associated the great fact of their geological 
history,—that these islands have, since the later tertiary periods, 
been in the process of elevation,—that they are the harbingers of 
a future continent, unlike the groups in the Pacific, which are the 
remains of ancient continents. Coincident with these two gene- 
ral facts in the West Indies is also a third,—that their coral reefs 
are all fringing, and that coral islands are wanting.” 
distribution of species. Among the ¢errestrial shells, typical 
_ forms exist in great profusion. These forms are of every con- 
_ geivable grade of value, from varieties up to genera and families. 
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