526 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



S s> Ii ;<■ r i ii iti p 1 a ii ii in , M. & H 



Plate 43, figs. 6, a, b. 

 Sphocrium planum, Meek and Hayden (1860), Proceed. Acad. Nat. Sci. Philad., 175 



Shell rather small, broad-oval or subcircular, much compressed ; extrem- 

 ities more or less regularly rounded, the posterior margin being sometimes 

 faintly subtruncated ; base semi-oval in outline; cardinal margin somewhat 

 straightened, or sloping gently from near the middle ; beaks very small, 

 compressed, scarcely extending beyond the hinge-margin, and nearly central ; 

 surface marked by line, irregular, obscure, concentric striae; lateral teeth 

 well developed. 



Length, 0.38 inch; height, 0.32 inch ; convexity, 0.08 inch. 



This species will be distinguished at a glance from all the others known 

 in these formations, by its remarkably-compressed form and small beaks, 

 which characters give it much the appearance of a little Lucina. I have 

 not seen any specimens showing the hinge very satisfactorily ; but some 

 internal casts retain distinct impressions of the lateral teeth, which seem to 

 be well developed. The cardinal teeth appear to be very small. 



Locality and position. — Near Grand Island, on the Upper Missouri ; 

 from the Judith River, or Brackish-water Lignite series: probably belonging 

 to the closing period of the Cretaceous. 



S p li se ri ii in I <> r tn o s n in , M. & H. 



Plate 43, figs. 4, a, b, c. 



Cyclasformosa, Meek and Hayden (1856), Proceed. Acad. Nat. Sci. Philad., VIII, 115. 

 Cyclas fragilis, Meek and Hayden, ib. 

 Sphceriumformomm, Meek and Hayden (1860), ib., 185. 



Shell small, rhombic-orbicular, moderately convex ; cardinal margin 

 nearly straight, and of medium length ; anterior side rounded ; posterior side 

 broader than the other, and truncated a little obliquely above, rounding 

 abruptly into the base below ; ventral margin semi-ovate, most prominent 

 behind, and rounding up more gradually in the front; beaks obtuse, a little 

 tumid, rising somewhat above the hinge, nearly touching, and located a little 

 in advance of the middle. Surface marked by small, rather distinct, regular, 

 concentric striae. 



Length, 0.17 inch; height, 0.14 inch; convexity, 0.08 inch. 



This species seems to be closely allied to S. corneum, Linn, (sp.), as 

 figured by Dr. TJeuss in Dunker and von Meyer's Palasontographica (II, pi. 



