2 A. EF. Verrill on the Mollusca of Europe and N. America. 
remark that, to an American, it seems rather singular that most 
European writers, whether zodlogists or botanists, find it 
necessary to trace back to a Kuropean origin all the existing 
species of this country, and to suppose that they have ‘mi- 
erated” 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 Hurope 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 Hurope 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 Huropean forms (whether 
terrestrial or marine) can be traced back into our Tertiary form- 
ations quite as far (if not farther) than they can in Kurope; 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 Hurope. 
Moreover the great number and diversity of the land and fresh- 
water shells of America (e. g., of Unionide, Melanie, &c.), and 
the peculiar facts in their geographical distribution, cannot but 
convince any one familiar with the subject that they have orzg- 
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 Kurope have had 
a history different from those that are still peculiar to America. 
Of course, no one will deny that certain species of land-shells 
have been introduced from Hurope 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 
HKurope, 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 Hurope or America. 
The following marine species (named as in Gould), which Mr. 
Jeffreys puts down as belonging to the region north of Cape | 
