STANTON I THE MARINE CRETACEOUS INVERTEBRATES. 9 



gions. Even if the Pueyrrydon species should prove to be identical with 

 the form from Portezuelo, which according to Behrendsen shows no es- 

 sential difference from the European species, I should not consider that 

 in itself sufficient proof of the Gault age of the beds containing it. 



One other of Behrendsen's horizons, " the Neocomian of the Arroyo 

 Triuguico and of Quili Malal," affords a slight basis of comparison. Two 

 of the Ammonites, Hoplites desori and H. neumayri, are somewhat sug- 

 gestive of two of the forms I have described as species of Hatchericeras 

 and they are referred to, or compared with some of the same European 

 species mentioned in my descriptions. It is evident, however, that none 

 of the forms figured by Behrendsen is identical with or very closely re- 

 lated to any of the Pueyrrydon ammonites. Several other genera are 

 represented in both this Neocomian and the Pueyrrydon fauna but the 

 species are not identical. 



Comparisons made with Cretaceous fossils described from other regions 

 along the Andes from Chili northward gave similar negative results, and 

 there are no indications of close relationship with North American Creta- 

 ceous faunas that are worthy of mention. 



The very close resemblance of one of the Pueyrrydon species of Tri- 

 gonia to T. ventricosa Krauss from the Uitenhage beds of South Africa 

 led to a close examination of the fauna of that formation, and while another 

 of its species, T. van, proved to be related to a Pueyrrydon form, and 

 there are superficial resemblances in the species of Gervillia, Astarte and 

 Ostrea, the fauna as a whole is too different to permit definite correlation. 

 The Uitenhage beds are now generally referred to the Lower Cretaceous, 

 though they were formerly assigned to the Jurassic. 



As it is impossible to correlate the Pueyrrydon series by means of 

 identical species, it is necessary to rely on more general comparisons, at- 

 tempting to give due weight to the somewhat conflicting evidence. 



Ammonites and Trigonias are usually among the most trustworthy 

 groups in determining the age of beds. In this case it has been thought 

 necessary to refer all the species of ammonites to a new genus whose re- 

 lationships are not very firmly established, but nearly all the species with 

 which these forms are compared occur in the Lower Cretaceous, and as- 

 suming that the genus is derived from Hoplites, or its near relatives, the 

 stage of development observed is what one would expect to find at that 

 period. Certainly no such forms are known later than the middle of the 

 Cretaceous. 



