TO JUNCTION OF GRAND AND GREEN RIVERS. 127 



angular. Under valve moderately convex. Upper valve nearly or quite flat Sur- 

 face of each valve ornamented by eighteen to twenty small, rather sharply-elevated, 

 plications, only about half of which extend to the beaks, while the intermediate ones 

 usually extend from one-third to one-halfway from the free margins; concentric 

 markings rather obscure. 



Length from beak to the most prominent part of ventral margin, 0.50 inch; trans- 

 verse diameter, 0.43 inch ; convexity, 0.11 inch. 



Resembles in size and form P. incongrua, Conrad (United States and Mexican 

 Boundary Report, vol. I, plate 6, fig. 10, 1857), but differs in not having squamose 

 concentric markings as well as in having shorter plications intercalated between those 

 thai extend to the umbo. The substance of the shell must be thin, since the plications 

 are rather distinctly marked on internal casts. 



Locality and position. — Oovero ; Lower Cretaceous of Dr. Newberry's section. 



Genus INOCERAMUS, Sowerby. 



[NOOBRAMTJS PEAGILIS, Hull and Meek. 



Plate [,fig.6. 



lnoc t ramus fra it \Us,]u\\ - AU ,\ Meek, M,,„. American Acad. Arte and s,-i, vol. 5, new "series, plate 2, fig. n. 



The specimens of this species in the collection an; larger than that first figured 

 and described by Professor Hall and the writer, which is evidently a young shell. 



They agree, however, so nearly in all other respects as to leave no doubts in regard to 

 their identity. In comparing the (inure here given with that first published in the 

 Memoirs of the American Academy, it should be borne in mind that the anterior side 

 <)f the latter was mistaken lor the cardinal margin, both in the description and in the 

 arrangement of the figure on the plate. The figure given on the accompanying plate 

 is correctly arranged, with the hinge-margin upward. 



This species has a wide geographical distribution in the far west, having been col- 

 lected at several distantly-separated localities between Fort Benton on Hie Upper 

 Missouri and Xew .Mexico in the far southwest. I have no knowledge of its occur- 

 rence anywhere east of the Mississippi. 



Locality andposition.—y&do del Chamo; base of the Middle Cretaceous of Dr. 



Newberry's section. 



Genus CRASSATELLA, Lam. 



('UASSATELLA SHT7MABDI, Meek. 

 Plate II, figs, 7 a, b, c. 



Shell under medium size, very thick, oval-subtri-onal, moderately convex; extrem- 

 ities narrowly rounded ; base forming a semi-oval curve; dorsal outline sloping from 

 the. beaks at an angle of about 100°; beaks moderated prominent, rather obtuse, 

 located slightly in advance of the middle; surface marked by fine lines of growth, 

 and small, regular, concentric ridges; escutcheon lanceolate ; lunule lance-oval, rather 

 deep; muscular scars strongly impressed. 



Length, 0.78 inch; height, 0.72 inch; convexity, 0.40 inch. 



