TABLE VTT. 



KOSSir, SHELLS OHAHACTHRTSTIC OF THK CT; F.TACKOUS I'OH JIATION ■IV NHI!T!ASKA. 



Figurrs 2. .">. 4. nnd T), Mednl-iuleil iVnm ilif Oi iy^iiKil Specimens. ' 



T:il). VII., Fig. 1. Ciicullaa Ncbrasccnsis (N. S.) Fox Hills. Ijetween the Cheyenne and Moieaii Rivers, NeVirnskn. 

 " Fis;. 2. Amnioyiiles Chcyemiensis (N. S.) Fox Hills, Nebraska. 



'• Fig. .3. Iiwccramus Sagensis (N. S.) Sage Creek, a soutliern tributary of tl je Clieyenne, Ijorilering on the confines 



of the Eocene Tertiary of Nebraska. 

 " Fig. 4. Scaphitcs comprimus (N. S.) Fox Hills, Nebraska. 



Fig. 5. Ammonites (1) Mandanensis, Morton. Fox Hills, between the Cheyenne and Morean Rivers, Nebraska. 



On comparing this fossil with Dr. Morton's figure and description of ./?. Mnnfianeiisis, fig. 2, PI. H., and 

 p. 208 of vol. viii., part 1, of the Joorn. Acad. Nat. Sci., I at first doubted whether it could be considered 

 of that species, inasmuch as the tubercles of the internal margins, and even those of tlie external mar- 

 gins, were represented so mnch more distinct than they appeared on the Nebraska fossil. However, 

 ( a comparison of the authentic specimens of A. Mandanensis in the Academy of Natural Sciences, con- 



vinced me that no specific distinction could be established. 

 If Scaphites can be shown to be a satisfactory genus,* tlien it seems probable that this fossil would 

 ranlv with that group of concamerated shells. It is true that the boat-shaped form, from the 

 deflection of the last half wliorl, is obscure, but still it lias a considerable general resemblance, and 

 the compressed form of fig. 4, and has the same kind of ribbing on the last half whorl, on which the 

 serrations of the sutures of chambers are not manifest. 

 " Fig. 0. Barulites (imnpi'essus ?). Sage Creek, tributary of the Cheyenne, Nebraska. 

 " Fig. 7. Barulites (undet.). Sage Creek, Nebraska. 



The surface of this fossil is waved, from broad and flatly-rounded ridges or eminences, wliich traverse it 

 obliquely, and which, in consequence of their being most prominent near 'lie margins of the longest 

 diameter, form a shallow channel, or rather give a compressed form to the surface at right angles to 

 the long diameter. The Baciilites ovufus of Say has a similar waved surface, but differs in the trans- 

 verse sectioir presenting a more wedge-shaped form. 

 ■" Fig. 8. Mould of Xifcma.^ Fox Hills, Nebraska. 



" Fig. 9. Mould of Pectunmlus. Fox Hills, Nebraska. ' • 



" Fig. 10, Jlvicula (undet.) Fox Hills, Nebraska. 



In form this Avicula approaches to A. candescens of Nelson, as figured by Gold fuss, from the cretaceous 



formation of Westphalia. Its breadth, however, is greater in proportion to the length of the shell. 



which is rhombic in form, and less oblique than Goldfiiss's figure, and is not proviiled. near the 



middle of the back, with minute tubercnlated costic. 

 " Fig. II. 0;?/(V'((/(/. (undet.) Fox Hills, Nebraska. ' ■ 



* For reniiuks on Ihis lieml. see Aiipcndix- in tijis Ke|uiil. p. OTd. 



