Boundary in South America. 31 



Advancing farther to the south with the comparative 

 review of the Eoca-Salamanca-deposits, apparently the 

 region of Lake Pueyrredon is another stage on this way. 

 Hatcher collected to the southwest of this lake, in sedi- 

 ments far beneath the Santa Cruz Beds, a specimen of 

 Gryphaea tarda Hutt., a species from New Zealand. But 

 according to v. Ihering 73 this shell has to be assigned to 

 Gryphaea burckhardti Boehm. Ameghino 74 as well as v. 

 Ihering 75 suggests that the whole series of sediments 

 from the Lower Cretaceous up to the Tertiary might be 

 represented in the region of this lake. 



It is known, furthermore, that in the upper course of 

 the Rio Sehuen (Santa Cruz) deposits of the so-called 

 Sehueneen are exposed, and Ameghino and v. Ihering 

 have several times pointed out this fact. In 1908, 

 Ameghino reported the finding of Loncosaurus argen- 

 tinus Amegh. near Par Aik together with the existence 

 of Ostrea guaranitica Ih. In 1907, v. Ihering 76 also pub- 

 lished a few details, while in his molluscan catalogue 77 

 he added three other species to the known ones. Thus, 

 at present the following five species establish correla- 

 tions between these exposures and the Roca-Salamanca- 

 Beds : 



Ostrea Clarce Ih. 



Ostrea guaranitica Ih. 



Corbula sehuena Ih. 



Potarnides patagonensis Ih. 



Struthiolaria sp. 



By these species the Sehueneen is sufficiently character- 

 ized as a part of the San Jorge-Formation, particularly 

 as Loomis recently found Ostrea guaranitica also in the 

 Salamanca of the surroundings of the Gulf of St. George. 

 The appearance of the freshwater-shell Diplodon (Unio) 

 colhuapensis was noted by v. Ihering. Hauthal found 

 this shell at the Rio Sehuen and it also appears in the 

 sediments around the Gulf of St. George, but I suppose 

 that it proceeds from the Pehuenche Beds beneath the 

 San Jorge. 

 Farther to the south, the oyster-banks of brown color 



73 Les mollusques fossiles, pp. 6 and 32. 



74 Les formations sedimentaires, p. 53. 



75 Les mollusques fossiles, p. 32. 

 70 Ibidem, pp. 49 etc. 



77 Katalog der Mollusken aus den Kreide- und Tertiarablagerungen Argen- 

 tiniens, enthalten in der Sammlung des Verfassers, Notas preliminares 

 editadas pela redaccao da Eevista do Museu Paulista, vol. 1, fasc. 3, Sao 

 Paulo, 1914. 



