No. 520] TERTIARY ARCHHELENIS 239 



existed at that time, there must have been a coast line 

 not only in the south, but also in the north of this land, 

 running across the present Atlantic from North Africa 

 to the West Indies. Since the forms under discussion 

 are most emphatically marine littoral-shells, such a coast 

 line would have favored their migration from the Euro- 

 pean waters to those of the West Indies and North 

 America. Thus these forms, which are found both in the 

 Patagonian and in the Indo-European Tertiaries, should 

 have been able, by all means, to reach also North Amer- 

 ica. The fact, however, that they are absent in the latter 

 parts indicates decidedly, that there was no possibility 

 for them to go across the Atlantic from Europe to Amer- 

 ica, and thus there can not have been a coast line or a 

 land connection between Africa and South America, but 

 there must have existed a deep ocean (the Atlantic), 

 which prevented their migration from Europe to North 

 America as well as from Europe by the direct way to 

 Patagonia. 



One fact, however, remains now unexplained, namely, 

 the absence of North American types in Patagonia. If 

 the Atlantic Ocean extended uninterruptedly from 

 north to south, as it does now, there must have been, dis- 

 regarding small interruptions at Panama and in the 

 region of the Amazonas, a rather continuous shore line, 

 along which the northern forms could have migrated to 

 Patagonia. I think such a north-south migration actu- 

 ally took place, but it did not reach the southern extrem- 

 ity of South America on account of climatic differentia- 

 tions along this coast line. Von Ihering points out (p. 

 492) that the Patagonian fauna is characterized by the 

 absence of certain types of shells, which are preeminently 

 tropical. This very strongly suggests that the Patago- 

 nian Tertiary seas were not of a tropical, but of a sub- 

 tropical or even temperate, character. If this is true, it 

 is apt to furnish an explanation for the absence of North 

 American forms in Patagonia. The North American 

 fauna of the Tertiary is found from Florida to New 



