Contributions to Palaeontology. 



115 



GASTEROPODA. 



GENUS PLATYCERAS (Conrad). 



PLATYCERAS PRIMORDIALIS ( n. s.). 

 PLATE I. FIG. 28. 



Shell rotund, rapidly expanding from the apex, and 

 spreading to a broad aperature : 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 showing the early existence of this form of G-astero- 

 pod. One or two other specimens 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 (Sowerby). 

 EUOMPHALUS? VATICINUS (,'n.s.), 

 PLATE I. 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 convex above. Another speci- 

 men 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. 



