Boundary in South America. 45 



Bouchardia patagonica Ih. Myochlamys patagonensis Ih. 



Turrit ella chilensis Sow. Venus (Chione) eupyga Ih. 



Gryphaea burckhardti Boehm Pododesmus Valehetanus 101 Ih. 



Malletia ornata Ih. Modiola andina Ortm. 



Besides 



Cardita patagonica Ih. 

 and 



Struthiolaria ornata Ih. 



species of the Patagonian Formation are represented in 

 the material proceeding from the region of the Rio 

 Grande. From the same point of view it is very remark- 

 able that v. Ihering 108 regarded the following species of 

 the San Jorge as forerunners of forms of the Patagonian 

 Formation: Ostrea rionegrensis as forerunner of 0. 

 hatcheri and Venericardia palaeo patagonica as forerun- 

 ner of V. inaequalis. 



Special interest is offered by the genus Panopaea. 

 According to Wilckens, 109 Panopaea inferior Wilck. is 

 represented in the Upper Senonian of South Patagonia 

 as well as in the Roca Beds, and I am inclined to hold 

 this form as identical with Panopaea nucleus Ih. of the 

 Patagonian Formation; or at least it must be admitted 

 that P. inferior Wilck. is the forerunner of P. nucleus Ih. 

 On the other hand, v. Ihering in his catalogue of 1914 (p. 

 63 and plate II, fig. 8) describes and figures a new Pano- 

 paea of the Salamanca-Beds (Rio Chico) : P. Thomasi Ih. 

 This form appears identical with P. inferior Wilck. I 

 believe that this species passes from the Upper Senonian 

 into the San Jorge and from there into the Patagonian 

 Formation, thus representing one of the most persistent 

 forms of this region. 



Without recourse to the very defective statistical 

 method, it seems to me that the foregoing data indicate 

 a strong Tertiary element in the San Jorge-fauna. The 

 sole elements, that perhaps could be regarded as Creta- 

 ceous, are the genera Exogyra, Gryplicea and Trigonia; 

 but none of these is decisive. The former two, although 

 scarce, are known from Tertiary formations, while Tri- 



107 See Les mollusques fossiles, p. 32. According to v. Ihering this shell 

 was found near Eoca and at Lake Pueyrredon. 



108 Les mollusques fossiles, p. 489. 



108 Die Meeresablagernngen etc., p. 143. 



