THE HISTORY OF THE NORTH ATLANTIC 87 



locomotive powers, even when young, but they are northern 

 forms not proceeding far south, so that they may have passed 

 through the Arctic seas. In this connection it is well to re- 

 mark that many species of animals have powers of locomotion 

 in youth which they lose when adult, and that others may have 

 special means of transit. I once found at Gaspe a specimen 

 of the Pacific species of Coronula, or whale-barnacle, the C. 

 regince of Darwin, attached to a whale taken in the Gulf of St. 

 Lawrence, and which had possibly succeeded in making that 

 passage around the north of America which so many navigators 

 have essayed in vain. 1 



But it is to be remarked that while many plants and marine 

 invertebrates are common to the two sides of the Atlantic, it 

 is different with land animals, and especially vertebrates. I do 

 not know that any palaeozoic insects or land snails or millipedes 

 of Europe and America are specifically identical, and of the 

 numerous species of batrachians of the Carboniferous and 

 reptiles of the Mesozoic, all seem to be distinct on the two 

 sides. The same appears to be the case with the Tertiary 

 mammals, until in the later stages of that great period we find 

 such genera as the horse, the camel, and the elephant appear- 

 ing on the two sides of the Atlantic ; but even then the species 

 seem different, except in the case of a few northern forms. 



Some of the longer-lived mollusks of the Atlantic furnish 

 suggestions which remarkably illustrate the biological aspect of 

 these questions. Our familiar friend the oyster is one of these. 

 The first-known oysters appear in the Carboniferous in Belgium 

 and in the United States of America. In the Carboniferous 

 and Permian they are few and small, and they do not culminate 

 till the Cretaceous, in which there are no less than ninety-one 

 so-called species in America alone ; but some of the largest 

 known species are found in the Eocene. The oyster, though 



1 I am informed, however, that the Coronula is found also in the Bis- 

 cayan whales. 



