DESCRIPTIONS OF NEW SPECIES. 129 



Genus CORBULA Bruguiere. 



Corlula subundifera (sp. nov.). Shell of ordinary size ; marginal out- 

 line subtrihedral or subovate ; valves only slightly unequal ; beaks con- 

 tiguous ; umbones moderately prominent ; beaks incurved and directed a 

 little forward; front obliquely truncate, concave, producing indistinctly 

 defined anterior umbonal ridges ; abruptly rounded below to the basal 

 margin, which is broadly rounded; posterior extremity low, prominent, and 

 sharply rounded; postero-dorsal margin sloping from the dorsum to the 

 posterior extremity ; this margin of each valve is bent abruptly inward and 

 downward, producing a narrow, shallow furrow, bordered at each side by a 

 somewhat prominent ridge, which extends from behind the beak- to the 

 posterior extremity of the shell. 



Surface marked by numerous, more or less strongly elevated, con- 

 centric folds, which disappear before reaching the anterior and posterior 

 margins. Between these folds, and upon those parts of the surface 

 unmarked by them, the surface is marked by ordinary lines of growth. 



Length, twenty-five millimeters ; height, eighteen millimeters. 



This species closely resembles C. undifer Meek, from the Point of Rocks 

 Group at Rock Springs, Wyoming, but differs from that species in its less 

 extended posterior extremity, its less angular posterior umbonal ridges, its 

 less sharply elevated, concentric folds, and in wanting the peculiar flattening 

 of the umbones between the posterior and anterior umbonal ridges which 

 that species possesses. 



Position and locality. Bitter Creek Group; Point of Rocks, Wyoming. 



Gasteropoda. 

 Genus SUCCINEA Draparnaud. 



Succinea papillispira (sp. nov.). Shell rather small, ovate or subelliptical 

 in lateral outline; spire minute but prominent; last volution much expanded 

 and broadly convex. 



Surface marked by the ordinary lines of growth, and, under a lens, 

 faint, close-set, revolving striae are to be seen. 



Length, eleven millimeters; breadth of aperture, six millimeters. 



9PG 



