IO PATAGONIAN EXPEDITIONS PAL/EONTOLOGY. 



Trigonia subventricosa belongs to a purely Cretaceous section which 

 has similar forms in the Upper Cretaceous, but the .most closely relatep 

 form is T. ventricosa from the Lower Cretaceous Uitenhage beds, which 

 also yield a form similar to the other Pueyrrydon species T. heterosculpta, 

 though another species which may belong to the same section occurs in 

 the Upper Cretaceous Quinquina beds of Chili. The evidence of both 

 Ammonites and Trigonias, therefore, seems to favor the Lower Cretaceous 

 age of the series. 



The specific characters of some of the other groups, such as the Ostrea, 

 the Gervillia, the Astarte species, the Pleuromya, and the Solecurtus (?) 

 also tend to place the beds below the middle of the Cretaceous. Certain 

 of the other forms, such as Cinulia, Tornatellaea, Lunatia, Martesia, Turnus, 

 Mactra (?), and Pinna, have a more modern aspect and would not be out 

 of place in an Upper Cretaceous fauna, while the remainder are mostly 

 of types that have a greater range within the Mesozoic. 



After my preliminary examination of this collection the opinion was 

 expressed 1 that the horizon represented is "about the middle of the Cre- 

 taceous, at least not lower than the Gault." This judgment was influ- 

 enced to some extent by the supposed occurrence in the collection of the 

 characteristic Upper Cretaceous genus Pugnellus. Further study of the 

 material after it was better cleaned showed that this generic identification 

 was incorrect, and the closer examination of the collection has in several 

 cases tended to emphasize the evidence for older rather than newer Cre- 

 taceous age. The former opinion is, therefore, now modified to this ex- 

 tent, that the horizon is not later than the Gault. Although the evidence 

 as above sketched and as given more in detail in the specific descriptions 

 does not seem to me to justify the definite reference of the Pueyrrydon 

 series to any one of the European Cretaceous horizons it is reasonably 

 certain that it belongs within the Lower Cretaceous and is not younger 

 than the Gault. 



1 Quoted by Hatcher, Am. Jour. Sci., 4th Ser., Vol. IX, p. 90, and published in abstract 

 of communication to Geological Soc. of Washington, Science, N. S., Vol. XI, p. 349, 1900. 



