132 VON IHERING — MOLLUSCAN FAUNA OF PATAGONIA. [Aprils, 



ON THE MOLLUSCAN FAUNA OF THE PATAGONIAN 



TERTIARY. 



BY H. VON IHERING. 

 (Plate XIX.) 



{Read April 3, 1902.) 



During the last ten years the exploration of the Patagonian and 

 Argentine Tertiary has been very actively prosecuted, but the 

 results of the new studies have not always represented genuine 

 progress. 



This refers particularly to the deposits of Entre Rios, which 

 Alessandri regarded as Eocene from his studies of Selachian teeth, 

 while A. Smith Woodward, reexamining the same material, came 

 to the conclusion that this formation is Miocene or Pliocene. The 

 study of the Mollusca of the Entre Rios beds led me to the opinion 

 that they are Miocene, while Borchert, in view of the large propor- 

 tion of recent species in this fauna, refers the formation to the 

 Pliocene. 



Having at my disposal one of the best collections of marine 

 shells from the Brazilian and Argentinian coasts, I have carefully 

 examined Borchert' s work. This author has had access to a much 

 richer collection of Entre Rios moUusks than I myself, in which are 

 represented well-preserved examples of some species — e. g., Cardium 

 magnum Born — of which I have seen only casts. This circumstance 

 does not, however, entirely explain the divergence of our opinions, 

 which is rather due to a number of incorrect determinations by 

 Borchert. The small shell which he believes to be Dione purpurata 

 Lam. is not referable to that species. The opinion that the young 

 shell differs in outline from that of the adult is refuted by the large 

 series of specimens in my collection. It is not reasonable to attach 

 much importance to such young shells, especially if represented 

 only by a single specimen. 



'* Cryptogramma brasiliana Gm." is not this species at all, but a 

 different and extinct species, characterized by its numerous coarse 

 concentric ribs, as also by numerous radiating strice. Beside these 

 two species, the following are certainly erroneously determined : 



