INVERTEBRATE PALEONTOLOGY. 155 



posterior side long and subtruncate at the extremity; dorsal outline nearly 

 straight, or declining slightly, with a long, gentle curve from near the beaks 

 posteriorly; beaks gibbous, very oblique or directed forward, noi much 



elevated. Ideated near the anterior end ; umbonal slopes quite convex from 

 near the beaks obliquely backward toward the lower part of the truncate 

 posterior, but not angular ; anterior muscular impression ovate, deep, and quite 

 well defined; posterior one broader and very shallow; surface unknown. 



Length (of cast), 0.92 inch; height, 0.G5 inch; breadth, or convexity, 

 0.55 inch. 



Our specimens being merely internal casts, with only portions of the 

 inner lamina adhering, of course give no idea of the, nature of the surface- 

 markings, and none of them show the .hinge. The shell has the general 

 aspect, however, of a depressed Veniella, and the muscular and pallia! 

 impressions are as in that genus. 



On the posterior side of the beaks, the internal cast is provided with a 

 distinct, broad, lanceolate depression, bounded on each side by a rather 

 prominent subangular 'ridge. This depression extends back nearly to the 

 truncated anal end, and seems to indicate the existence of a rather strong 

 hinge-margin, and well-developed posterior lateral teeth. The pallial line is 

 quite distinct, and, instead of forming a regular curve in descending from the 

 posterior muscular impression, passes first nearly straight downward, and 

 then makes an abrupt turn forward parallel to the base. 



Locality and position. — Yellowstone River: in beds .containing a blending 

 of the fossils of the Fox Hills and Fort Pierre groups. 



Veniella (Tenilicardia!) Immilis, M. & H. 



Plate 30, figs. 5, a, b, c. 



Cyprina hvmilis, Meek and Haydeu (May, 1860), Proceed. Acad. Nat. Sci. Philad., VIII, 170. 

 Venilia humilis, Meek (1804), Smithsonian Check-List North Am. Cret. Fossils, 13. 



Shell transversely ovate, gibbous, thick, very oblique; anterior side 

 scarcely extending beyond the beaks, abruptly rounded below: base semi- 

 ovate in outline, most prominent toward the front, sometimes a little 

 contracted behind; posterior side long, rounding obliquely with a broad 

 curve from the dorsum to the postero-basal extremity, which is narrow l\ 

 rounded; beaks very oblique, almost overhanging the anterior border, 

 declining and curving inward at the extremities; lunule excavated, but not 

 defined; umbonal slopes prominent from near the beaks obliquely backward 



