NATURAL SCIENCES OF PHILADELPHIA. 423 



Oslrea subovata (= 0. Marshii, Marcou), 0. carinata, 0. quadriplicate, Janira Tex- 

 ana, J. Wrightii, Tnoceramus problematicus, Pachymya Austincnsis, Lima crenulico- 

 sta, Terebratula Wacoensis, Turrilites Brazoe?isis, Ammonites Texanus, A. Brazo- 

 ensis, Hamites Fremonti, and Nautilus Texanus. 



Relations of the Lower Cretaceous series of Nebraska to subdi- 

 visions at foreign localities. Having now considered, in the order of their 

 succession, the several rocks embraced in the Lower Series of the Nebraska 

 Cretaceous deposits, and endeavored as far as our present means of investigating 

 the subject enables us to do, to trace out their relations to the Cretaceous beds 

 of other parts of this country, it will be interesting to see how nearly their syn- 

 chronism with known horizons in the Cretaceous system of the old world can 

 be traced out. With this view we have carefully compared with European 

 forms all the fossils in the several Nebraska collections from these rocks, in- 

 cluding those most recently obtained, to which the new species described in 

 this paper belong. These comparisons have satisfied us that the formations 

 under consideration, that is, the Niobrara Division, Fort Benton Group, and 

 the Dakota Group, represent together the Lower or Gray Chalk, and probably 

 the Upper Green Sand of British geologists (= Turonien and Cenomanien, of D'Or- 

 bigny.) We had in 1856, identified the Gray Chalk species Inoceramus problema- 

 ticus in the Niobrara Division (No. 3 of former sections), and suggested that this 

 rock probably holds a position at about the horizon of the Lower Chalk of the 

 old world.* More recently we had likewise mentioned that we regarded Am- 

 monites percarinatus, Hall & Meek, as being probably identical with the well 

 known Lower Chalk species A. Woolgari of Mantell.f These facts, however, 

 had not so forcibly attracted our attention until we commenced the investiga- 

 tion of the collections containing the new species described in this paper. 



The evidence upon which we have placed these rocks on a parallel with the 

 Lower or Gray Chalk of British geologists, will be more clearly understood by 

 consulting the following list of species from them, which are either identical 

 with, or so closely allied to, species found in that position in the old world, as 

 to be safely regarded we think, as contemporaneous representative forms : 



Found in the Lower Serie3 of Nebraska. European Lower Chalk species. 



Ammonites vespertinus Mort.,. represents A. Rholomagensis Defr., & other L. Chk. sp. 



A. percarinatus H. & M., probably ident. with A. Woolgari of MantelL 



Scaphites Warreni M. & H.,... scarcely distinct from S. cegualis Sowerby. 



S. larvceformis M. & H., same type as " 



Nautilus elegans var., can scarcely be distinct from N. elegans Sowerby. 



Inoceramus latus? appears to be the same as /. latus of Mantell. 



Inoceramus probhmaticus% can not be distinguished from I. problematicus, 



[Schlot. sp. 



Inoceramus problematicus is most frequently met with in the Niobrara division, 

 but is also sometimes found in the Fort Benton Group : all the others are 

 generally peculiar to the latter rock in Nebraska. Inoceramus latus, Ammonites 

 vespertinus, and a species very closely allied to Nautilus elegans, are found 

 in Texas in beds apparently representing the Niobrara division. Other species 

 from our Lower series of Nebraska similar to Lower Chalk forms of the old 

 world, might be mentioned, but the foregoing list includes the most striking 

 examples. 



We may, however, state that, with a few doubtful exceptions, nearly all the 

 other species yet known in the lower series of Nebraska Cretaceous rocks, pre- 

 sent much nearer affinities to Lower Chalk forms than to species holding a 



* Proceed. Acad. Nat: Sci. Phila. Nov. 1856, p. 267. 



t Proceed. Acad. Nat. Sci. Phila. October, 1860. p. 419. Mr.Gabb has also suggested in 

 a note 10 p. 129, of his Synopsis ot Cret. Foss. that the rocks under consideration may re- 

 present the Lower Chalk of England. 



{This species is said 10 also occur in the Upper Green Sand of Europe. 



1861] 



