416 GEOLOGY OF THE BLACK HILLS. 



SINUOPALLIA. 



VENERIim 



Genes DOSINIA Scopoli. 



DOSINIA MISSOURIANA % 



Plate 11, figs. 25, 26. 



? Cyiherea missouriana Morton, Jour. Acad. Nat. Sci. Phil., vol. 8, PI. xi, fig. 2. 



? Cytherea missouriana (Morton) M. & H., Proc. Acad. Nat. Sci. Phil. Nov. 1856, p. 20. 



f Dione missouriana (Morton) Meek, Check List Invert. Foss. Smithsonian Inst., p. 13. 



Cytherea deweyi M. & H., Proc. Acad. Nat. Sci. Phil., vol. 8, p. 83. 



Merctrix deweyi M. & H., Proc. Acad. Nat. Sci. Phil., vol. 12, p. 185. 



Callista deweyi M. & H., Proc. Acad. Nat. Sci. Phil., vol. 13, p. 143. 



Dione deweyi Meek, Smithsonian Check List Invert. Foss., p. 13. 



Callista {Dosciniapsis f) deweyi M., Pal. U. S. Geol. Sur. Terr., p. 182, PI. 17, fig. 15. 



Shell rather below a medium size, transversely subtriangular in outline, 

 with ventricose valves, which are most elevated on the umbones and grad- 

 ually declining toward the basal line; being cuneately cordate in a section 

 from the beaks to the basal line where the valves are united. Beaks of 

 moderate size, or for the size of the shell somewhat large, pointed, incurved, 

 and directed forward, situated much nearer the anterior end ; posterior 

 cardinal line arcuate ; posterior and anterior extremities of the shell rather 

 sharply rounded, the anterior most distinctly so, and the cardinal line on 

 this side slightly contracted below the beaks ; basal line broadly curved, 

 more abruptly rounded toward the extremities. 



Surface marked by fine, irregular lines of growth ; muscular impres- 

 sions large and submarginal. Pallia] line deeply sinuate, the sinus acutely 

 angular, and directed obliquely forward and upward, reaching to a little 

 behind the middle of the valve. 



The specimens of this species in the collection are in rather poor con- 

 dition, having the shell considerably exfoliated and broken, but they reveal 

 the form of the muscular imprints and pallial line very satisfactorily. The 

 structure of the hinge plate, however, cannot be made out. The subtri- 



