THE MARINE CRETACEOUS INVERTEBRATES. 



BY 



T. W. STANTON. 



THE fossils discussed in the following pages were collected in March, 

 1899, by Mr. J. B. Hatcher, in charge of the Princeton Expedition 

 to Patagonia, and it is through his kindness and the generous 

 courtesy of Prof. W. B. Scott that I have had the privilege of studying 

 the collection, which, though not large, has proved very interesting. 



In a paper entitled "Sedimentary rocks of southern Patagonia," Mr. 

 Hatcher 1 has described the section from which the fossils were obtained, 

 and named the various Cretaceous horizons recognized. The entire col- 

 lection came from two localities, only a few miles apart, in the neighbor- 

 hood of Lake Pueyrrydon, south latitude 47 30', west longitude 72. 

 One of the localities is four miles east of Lake Pueyrrydon, near the 

 mouth of the canon of Rio Tarde, a small stream emptying into the east 

 end of the lake. The other locality is about ten miles east of the same 

 lake, and about two miles south of the western border of White Lake. 2 



The following description of part of Mr. Hatcher's section along the 

 Rio Tarde is condensed from his account and gives only the features es- 

 sential to the present discussion.. The series about 750 to 800 feet in 

 thickness that includes all the fossiliferous Cretaceous horizons is called 

 the Pueyrrydon series. In it four formations are recognized, in ascending 

 order as follows : 



i. The Gio beds, consisting of 100 feet of soft green sands or marls 

 with several harder, brown layers, each about two feet thick and full of 

 the large Ostrea tardensis, with occasional specimens of a Lithopliagtis, 

 form the lowest horizon exposed. 



1 Am. Jo2tr. Sci., 4th Sen, Vol. IX., pp. 85-108, Feb., 1900, with a map of southern Patagonia. 



2 These geographic features are all shown on the map accompanying the paper just cited. In 

 the descriptions of species the locality labels accompanying the fossils are copied. 



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