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 

 so extraordinary and unexpected, may be considered as one of 

 the most interesting facts clearly established by the advance of 

 modern science." — p. 590. {Eighth 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 

 Europe. We may mention, by way of illustration, the total 

 absence of all allusion to the topic, in the interesting ^^Introduc- 

 tion to Conchology,^^ of Dr. George .Johnston. [London^ 1850.) 

 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 m which we may find descrip- 

 tions of any considerable proportion of the whole number of the 

 shells of the United States." lu his " Recapitulation," Dr. Gould 

 particularizes 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 

 point of land has hitherto proved a barrier to the 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 

 asserts, that of the 197 marine species then known, 83 do not 

 pass to the south shore, and 50 are not found on the north shore 

 of the Cape. 



Professor Adams in his " Second Annual Report on the Geol- 

 ogy of the State of Vermont,'''' {Burlington, 1846,) notices par- 

 ticularly the geographical distribution of species as a subject of 

 great importance in its application to geology. He enters on the 

 question of the foraier existence of gigantic mammalia on this 

 continent, and the time when they flourished, a subject variously 

 treated by other authors, and refers to the evidence afforded by 

 an examination of fossil shells. He concludes that those quadru- 

 peds, although found "to have been mired in shell marl, which 

 consists of the same species of freshwater shells, which now in- 

 habit our waters," did not belong to the present geological period. 



In 1848, Professor Agassiz and Dr. Gould published the first 

 part of their " Principles of Geology,''^ (Boston, 1848,) in which 

 a chapter is devoted to a consideration of the "Geographical 



