﻿2 A. E. Vern'U on the Mollusca of Europe and N. America. 



remark that, to an American, it seems rather singular that most 

 European writers, whether zoologists or botanists, find it 

 necessary to trace back to a European origin all the existing 

 species of this country, and to suppose that they have '' mi- 

 grated" from Europe to America and other countries in spite of 

 opposing currents and all other obstacles. Thus Mr. Jeffreys 

 can imagine that our land and freshwater shells could have mi- 

 grated from Europe all the way across Asia, the Pacific Ocean 

 and North America in order to reach Canada and New England; 

 but he does not seem to think it possible that they may have 

 originated in America, and thence crossed to Europe in the di- 

 rection of the prevailing currents and winds. Nevertheless 

 geology teaches us that America was a great continent, in very 

 early ages, when Europe was only a group of islands ; that no 

 other country is richer in the remains of terrestrial animals and 

 plants connecting the Tertiary and Cretaceous ages with the 

 present ; that many of these supposed European forms (whether 

 terrestrial or marine) can be traced back into our Tertiary form- 

 ations quite as far (if not farther) than they can in Europe ; and 

 that many of the genera of animals, and especially of plants, 

 now found living in both countries, can be traced back to the 

 Cretaceous in America and only to the Tertiary in Europe. 

 Moreover the great number and diversity of the land and fresh- 

 water shells of America (e. (/., of XJnionidcB^ Melanice^ &c.), and 

 the peculiar facts in their geographical distribution, cannot but 

 convince any one familiar with the subject that they have orig- 

 inated in America at a very remote period ; which is confirmed 

 by the fact that many of these can be traced far back into our 

 Tertiary formations. Nor are there sufficent reasons for sup- 

 posing that those of our species living also in Europe have had 

 a history difl'erent from those that are still peculiar to America. 



Of course, no one will deny that certain species of land-shells 

 have been introduced from Europe in modern times by human 

 agency ; but, so far as most of the identical species are concerned, 

 it seems to us far more probable that America gave them to 

 Europe, rather than the contrary, and this whether animals or 

 plants, terrestrial or marine. 



But the special errors to which I wish to call attention occur 

 in the table of species, showing their geographical distribution. 

 These relate both to the names and specific identity of certain 

 shells, and to their geographical distribution. Although not 

 agreeing with the author in regard to many of his remarks con- 

 cerning the generic relations and names of species, I do not pro- 

 pose to discuss them here ; for there seems to be no danger of 

 their general adoption, either in Europe or America. 



The following marine species (named as in Gould), which Mr. 

 Jeffreys puts down as belonging to the region north of Cape 



