ATPENDIX. 



The descriptions of the following two species, accidentally omitted in 

 their proper places in the body of the work, are added here. 



Telliiia (Arcopagia)! Clieyeiinciisis, M. & H. 



Plate 17, fig. 16. 

 Tellina ? Cheycnnensis, Meek and Hayden (1856), Proceed. Acad. Nat. Sei. Pbilad., VIII, 82. 



Shell transversely ovate, compressed, very thin ; anterior margin 

 rounded ; 'posterior margin faintly subtruncated, or rounding from above to 

 the very narrowly rounded or subangular posterior basal extremity ; basal 

 outline semiovate ; beaks rather prominent, placed a little in advance of the 

 middle; umbonal slopes prominently rounded from the umbones to the pos- 

 terior basal extremity ; surface ornamented with fine lines of growth, and 

 somewhat stronger little ridges and furrows near the lower margins. 



Length, 0.88 inch ; breadth, 0.36 inch ; height, 0.67 inch. 



This shell was originally referred (with a mark of doubt) to the genus 

 Tellina, merely because its hinge was unknown, and it resembles certain 

 forms from the Cretaceous rocks usually described under that name by some 

 reliable authorities, and not because it was really believed it to be a true 

 Tellina. In form and general appearance, it more nearly resembles Arcopa- 

 gia; but as no specimens have been seen showing its hinge and interior, 

 it is not possible to determine whether or not it even belongs to the 

 TeUinidcu. It is certainly not a true Tellina. 



Locality and position. — Forks of Cheyenne River, Dakota ; from the 

 Fort Pierre group of the Upper Missouri Cretaceous series. 



Ammonites?! Unllauanns, M. & H. 



Plate 8, figs. 1, a, b, c. 

 Ammonites Mullananus, Meek and Hayden (1862), Proceed. Acad. Nat. Sci. Philad., XIV, 23. 



Shell cotnpressed-subglobose ; rounded on the periphery ; umbilicus 

 small, deep, and acutely conical, between one-third and one-half as wide as 



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