TO JUNCTION OF GRAND AND GKEEN 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 Avhich extend to the beaks, while the intermediate ones 

 usually extend from one-third to one-half way 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. 1, plate 6, fig. 10, 1857), but differs in not having squamose 

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

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

 are rather distinctly marked on internal casts. 



I, nr<il it u inn! jHiNitiou. Covero ; Lower Cretaceous of Dr. Newberry's section. 



Genus INOCERAMUS, Sowerby. 

 INOCEBAMUS FRAGiLis, ITjill and Meek. 



Plato I, fig. 6. 

 Inooeramus fragilia, Hall anil Meek, Mom. American Acacl. Arts and Sci., vol. 5. now series, plate 2, fig. 6. 



The specimens of this species in the collection are 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 figure here given with that first published in the 

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

 of the latter was mistaken for 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 npward. 



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

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

 Missouri and New Mexico in the far southwest. I have np knowledge of its occur- 

 rence anywhere east of the Mississippi. 



Locality and position. Vado del Chamo ; base of the Middle Cretaceous of Dr. 

 Newberry's section. 



Genus CRASSATP;LLA, Lam. 



CRASSATELLA SHUMARDI, Meek. 



Plato II, figs. 7 a, I, c. 



Shell under medium size, very thick, oval-subtrigonal, 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 moderately 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 

 deej) ; muscular scars strongly impressed. 



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



