NATURAL SCIENCES OF PHILADELPHIA. 431 



rican form will probably prove to be only an allied representative species. In 

 addition to the above, we likewise find a Gryphoza in our Fort Pierre Group, 

 which presents close relations to G. vesicularis, if it is not indeed that species. 



When we come to the equivalent rocks further eastward, however, in New 

 Jersey, and at localities in Alabama and other Southern States, we are no 

 longer compelled, as previously stated, to rely upon doubtfully identical, or 

 closely allied representative species, for we there find a number of our Ne- 

 braska forms associated with some seven or eight well known European Upper 

 Chalk species. 



So far as we have been able to ascertain, the list given below embraces the 

 species known to be common to the New Jersey and Alabama rocks alluded to, 

 and the Upper Chalk and Maestricht beds of the Old World : 



Names. American Localities. Foreign localities and position. 



Saurocephalus lanciformis, New Jersey. England, White Chalk. 



Lamna acuminata, New Jersey. England, White Chalk. 



Befemnitella mucronata, New Jersey, Ala., &c. Eng., Fr., &c, Wh. Ck. & 



Maest. B. 

 Neithea Mortoni, New Jersey, Ala., &c. Fiance, White Chalk. 



Ostrea larva, N. J., Teim., Ala., &e. Eng., France, &c, Wh. Ck. 



& Maest. B. 

 Gryphcea vesicularis,* N. J., Tenn., Ala., &c. Eng., France, &c, Wh. Ck. 



& Maest. B. 

 Nucleolites crucifer, New Jersey. France, White Chalk. 



It is true we have in this upper series in Nebraska and further east, a few 

 forms allied to Lower Chalk and Upper Green Sand species, and we have re- 

 garded two of these, at least, as probably identical with foreign species of that 

 age. That is, we had supposed our Cucidloca Shumardi probably identical 

 with the Green Sand species, C. fibrosa of Sowerby, and a small Micrabacia 

 from our Fox Hills beds, probably identical with M. coronula Goldfuss sp., 

 from the same horizon. Later comparisons, however, have led us to regard 

 the latter as a distinct species ; and although we have not yet been able to 

 find characters by which our Cucullcea Shumardi can be distinguished from 

 the figures and descriptions of Sowerby's species we have seen, it is quite pro- 

 bable that a careful comparison of a series of good specimens would bring to 

 light constant differences of specific importance. Should these, however, and 

 several others we have from time to time compared with Green Sand and 

 Lower Chalk species, really prove to be undistinguishable from them, still 

 the weight of evidence would, on the whole, be strongly in favor of the con- 

 clusion that these rocks are certainly of the age of the Upper Chalk and Maes- 

 tricht beds. 



From all the foregoing facts it may be seen, first, that the only strongly 

 marked palseontological break in the Nebraska Cretaceous Section, so far as 

 we now know, is that dividing the Niobrara Division from the Fort Pierre 

 Group. 



Secondly, That all the Nebraska Cretaceous beds below this line, included 

 in our section, as well as the bed f. of the New Jersey Section, on page 426 of this 

 paper, represent the Lower or Gray Chalk, are probably the Upper Green 

 Sand of the Old World, f 



Thirdly, That all the Nebraska beds between this strongly marked line, 

 near the middle of the section, and the Tertiary, as well as the beds b, c, d, 



* This species is supposed by some to occur also in the Upper Green Sand, and the 

 Lower or Gray Chalk, but the form occurring in these lower positions is regarded by 

 other authorities as a distinct species. 



t By this remark we do not mean to express the opinion that Cretaceous strata older 

 than the Tpper Green Sand of Europe may not exist, and yet be discovered in 

 Nebraska and New Jersey. 



1861.] 



