XLVI INTRODUCTORY REMARKS. 



them with the European members of the Cretaceous system, as developed 

 there, with the view of determining their proper horizon in the same, it 

 becomes necessary to view them as forming together one natural division. 

 When thus considered, it becomes clearly evident, as has long been 

 known, that they represent the Upper or White Chalk of Europe. A longer 

 list of species from these American upper divisions identical with, or so 

 closely allied to, European White Chalk forms, as to be safely viewed as rep- 

 resentatives of the same, might be made out; but the following few ex- 

 amples will, perhaps, be sufficient: 



SP. FROM FT. PIERRE AND FOX HILLS AMERICAN LOCALITIES. FOREIGN LOCALITIES AND 



GROUPS, AND EQ. REDS. POSITIONS. 



NuclcoKtea crucifcr. Morton New Jersey Occurs in White Chalk of Fiance. 



Osirca larva, Lam Dak., New Jersey, Alab.,ctc England, France; White Chalk 



anil Maestricht beds. 



Neitliea Mortoni, d'Orb New Jersey, Alabama, etc France; White Chalk. 



Gryphaa reticularis, Lam New Jersey, Tennes., Alab., etc England, France, etc. ; White 



Chalk and Maestricht beds. 

 Inoceramus Sardbini, Mort Dak., New Jersey, Alab., etc Near I. Cripsii, Mant. ; White 



Chalk, England, etc. 



liaculites aneeps, Lam Wyom., New Jersey, Texas? White Chalk of Europe. 



Nautilus Delayi, Mort Dakota.New Jersey, etc Near X. hvciyaius, d'Orb., and 



allied White Chalk species. 

 Scaphitcs Conradi, Mort. Dak., Mont., New Jersey, Alab., etc. . Very like S. pulcherrimus, Roem. ; 



White Chalk, Germany. 

 ScapMtea nodosus, Owen Dak., Mont., Colorado, etc Near S. connlrictus, Sow., and S. 



compressus, Sow.; WhiteChalk, 



EDgland and France. 



Sphenodiscus 7t »/ie« fun's, Owen (sp.) . .Dakota, Colorado, etc White Chalk, Limbonrg. 



Belemnitella mucronata, Sch New Jersey, Alab., Miss., etc Widely extended in White Chalk 



of Europe; also in Maestricht 



beds. 



It is true that we have from these upper beds a few forms most nearly 

 allied to Lower Chalk and Upper Green-sand species, such for instance as our 

 Micrabacia Americana, nearly related to the European M. coromda, from the 

 Upper Green-sand, and our Cucullaa Shwnardi, closely resembling C. fibrosa, 

 Sowerby, from the same horizon. On the other hand, our Websteria cretacea, 

 from the Fox Hills group, has no known representative in the Old World but W. 

 crisioides of Edwards and Haime, from the Eocene of England, and Ostrea 

 (Gryphostred) vomer, Morton, which is scarcely distinguishable from O. eversa, 

 Deshayes, from the. same horizon. As a whole, however, the fauna of these 

 beds, as already shown, clearly and unmistakably represents that of the 

 Upper or White Chalk of the Old World. 



From the foregoing facts, it will be seen that the most strongly-marked 

 palseontological break in the Upper Missouri Cretaceous section, given farther 



