136 SIXTEENTH REPORT ON THE CABINET OF NAT. HISTORY. 



GASTEROPODA. 



GENUS PLATYCERAS (Conrad). 

 PLATYCERAS PRIMORDIALIS ( n. s.). 



PLATE VI. FIG. 28. 



Shell rotund, rapidly expanding from the apex, and spreading to 

 a broad aperture : volutions about one and a half. 



The specimen figured is a cast in friable sandstone, preserving scarcely 

 more than evidence of its generic relations. It is chiefly interesting as show- 

 ing the early existence of this form of Gasteropod. One or two other speci- 

 mens only have been observed : they occur in gray sandstone with greenish 

 particles on the Kickapoo river, and at Trempaleau, in a position below 

 the middle of the formation. 



GENUS EUOMPHALUS (^owerby). 

 EUOMPHALUS? YATICINUS ( n. s.). 



PLATE VI. FIG. 29. 



Several specimens of a euomphaloid shell have been found in 

 the sandstone of the Mississippi valley. One of these preserves 

 about four volutions of regularly increasing size, and gently con- 

 vex above. Another specimen shows a deep umbilicus, with the 

 volution a little flattened on the lower side, and subangular on 

 the periphery and umbilical margin. 



These imperfect specimens are characterized only for the interest attached 

 to their geological position and association. 



Fig. 29. The upper side of a somewhat distorted specimen, from the upper portion of 

 the formation at Lagrange mountain. 



