T. Bland on the Geographical Distribution of Mollusca. 391 
That author justly observes, that “the extent of this parcelling 
out of the globe amongst different nations, as they have been 
termed, of plants and animals—the universality of a phenomenon 
$0 extraordinary and unexpected, may be considered as one of 
most interesting facts clearly established by the advance of 
Modern science.”—p. 590. (Highth edition, London, 1850. 
The geographical distribution of shells (to which portion of 
the animal kingdom our remarks will be confined) has received, 
- and continues to receive much attention on the part of American 
Naturalists,—indeed more so, it would seem,: than from those of 
urope. We may mention, by way of illustration, the total 
absence of all allusion to the topic, in the interesting “ Jntroduc- 
tion to Conchology,” of Dr. George Johnston. (London, 1880.) 
The first direct reference to the subject in works of authors of 
the United States, is, we believe, in Dr. Gould’s Report on the 
Invertebrata of Massachusetts, (Cambridge, U.S., 1841.) In 
his Introduction, he says,—‘“No attempt has hitherto been made 
to give an account of-all the shells of any particular region on 
this continent. No book exists in which we may find deserip- 
tions of any considerable proportion of the whole number of the 
shells of the United States.”’ In his “ Recapitulation,” Dr. Gould 
particnlarizes the following instance of geographical limitation 
occurring in the state of Massachusetts: “Cape Cod, the right 
arm of the Commonwealth, reaches out into the ocean some fifty 
or sixty miles. It is nowhere many miles wide ; but this narrow 
he migrations of 
“Many species of Mollusca. Several genera and numerous spe- 
cies which are separated by the intervention of only a few miles 
of land, are effectually prevented from intermingling by this Cape, 
and do not pass from one side to the other.” p. 315. Dr. Gould 
asse 197 ine species then known, 83 do not 
eas ad oi found on the north shore 
peds, although found “to have been mire 
Consists of the same serge ” 
habit ” did not belong | 
Tn isis, hate pete and Dr. Gould published the first 
part of their “ Principles of Geology,” ( Boston, 1848,) in which 
& chapter is devoted to a consideration of the Geographical 
4 
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