528 THE AM ERIC AX NATURALIST [Vol. XLIII 



completely in upper Eocene times. They could just as 

 well have come from the Pacific, which seems to have 



Xot only are these northern invaders present in the 

 Chilean deposits on the Pacific coast, there are many 

 genera in the latter according to Dr. von Ihering, 38 such 

 as Conus, Purpura, Oliva, Cassis, Cypnea and Littorina 

 which never penetrated as far east as Patagonia at all. 

 They thus denote the manner of dispersal of all the 

 northern forms from north to south, and it appears as if 

 thev had graduallv crept southward along some ancient 

 coast line. But since there is no reason to suppose that 

 the present Pacific coast of South America had come into 

 existence already in early Tertian' times, we may assume 

 that the ancient coast line lay farther west. 

 Down to Miocene times the influence of the Caribbean 



northern Atlantic forms are traceable in the Tertiary 

 deposits all along the Pacific coast of South America as 

 far south as northern Chile and even on the Atlantic side 

 of the continent in Patagonia, which then freely com- 

 municated by a marine channel with the Pacific. 



On the other hand, the Tertiary molluscs of Chile and 

 California are very distinct from' one another. This ap- 

 parently implies that a barrier was interposed between 

 the northern coasts of California or rather between the 

 main portion of the Pacific coast line of North America 

 and that of South America. Hence it tends to support 

 my argument, that western Mexico and part of lower 



