322 PATAGONIAN EXPEDITIONS I PALAEONTOLOGY. 



plata, and the Payta-Tumbez beds near the southwestern extremity of 

 Archiamazonas : at these places we have probably these two continents 

 at their points of nearest approach to each other, and an exchange of 

 marine forms may have been possible. This exchange, however, was 

 rendered more difficult by climatic conditions, and especially, although 

 possible in a certain degree between the Ecuadorian and the Chilian prov- 

 ince, it was hard for the Caribbean and Ecuadorian fauna to migrate far- 

 ther south, into the Patagonian region. 



This leads us to investigate the probable climatic conditions of Pata- 

 gonian times. There is no doubt that in Miocene time, when the Pata- 

 gonian beds were deposited, a considerably warmer climate prevailed in 

 these regions, a fact that has been recognized by all previous writers on 

 this question (see for instance v. Ihering, 1897 b, P- 535)- Of the fossils 

 of the Patagonian beds the following point to a warm, tropical or sub- 

 tropical climate: Scutella, Perna, Cucullcea, Dolium, Ficula, Mtirex sub- 

 gen. Phyllotonus, Terebra, Drillia, Borsonia. A part of these genera has 

 also been found in the Navidad beds. On the other hand, a number of 

 characteristic tropical genera are missing in the Patagonian beds, which 

 have been found in the corresponding Chilian beds, for instance : Conus, 

 Mitra, Oliva, Cyprcea, Cassis, Columbella. Of these, Mitra, Oliva, and 

 Columbella are represented in the Miocene of northern Peru, and the pres- 

 ence of a Strombus in the latter beds (upper Miocene) points still more to 

 a truly tropical character. 



Thus we may say that the Patagonian beds although still retaining a 

 subtropical character differ distinctly from the Navidad beds in the lack 

 of some features, which depend probably on the climatic conditions, and 

 that the Navidad beds approach in just these features the tropical depos- 

 its of the Caribbean province, where genera like Conus, Strombus, Mitra, 

 Oliva, Columbella, Cyprcea form a very prominent element of the fauna. 



In this connection we may also mention the complete and very singular 

 lack of the genus Cerithium in Patagonia. The Navidad beds contain 

 only a single species of this genus, which is in striking contrast to the 

 contemporaneous deposits of the northern hemisphere. 



While we thus should claim for the Patagonian beds at least a sub- 

 tropical climate, we have, on the other hand, in them the beginning of a 

 differentiation of an "Antarctic" fauna, or, more properly, speaking, of an 

 extratropical fauna of the southern hemisphere, which is a pendant to, but 



