358 EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



CEPHALOPODA. 



Genus BELEMNITES, Lamarck. 



Belemnites denstjs, Meek and Hay den. 



Plate 3, fig. 4, a. b. 



Belemnites densus, Meek and Hayden (March, 1858), Proceed. Acad. Nat. Sci. Philad., X, 58 ; also (1865), Palyeont. Upper 



Many imperfect specimens of this species were collected from the Jurassic rocks 

 on the North Platte, near the Red Buttes. They agree exactly in all respects with 

 those brought by Lieutenant Warren's expedition from the Jurassic beds at the south- 

 west base of the Black Hills. This species is very closely allied to forms found in the 

 Jurassic deposits of France and Russia; and may, on comparison, prove identical with 

 some one of these foreign species. I have never yet seen an entire specimen of it, 

 though it is quite abundant, and all parts of it can be seen in detached fragments. It 

 probably attained a length of about 4.50 to 5 inches. 



CRETACEOUS FOSSILS. 



LAMELLIBRANCHIATA 

 Genus INOCERAMUS, Sowerby. 

 Inoceramus pkoblematicus, Schloth. 



tt (1820), Petrefact., 312. 

 Brong. (1822), Geol. des Envir. de Paris, 215, pi. 

 ides, Mantel (1822), Geol. Sussex, tab. xxvii, l 

 Conch., v, 61, 442.— Goldf. (1836), Betref. Gem 



, III, Terr. Grot., 510. 40<,--M< t k ;md ILmhm (1857), Proceed. 

 »k (1864), Smithsonian Ch.-.-k-l.Ut \. Am. fret. Fossils.-Meek, 



Shell rhomboid-ovate, oblique, moderately convex; anterior margin truncated 

 above, from the beaks at first obliquely backward and downward, thence passing by 

 a gentle oblique curve into the Wis.*; posterior margin descending obliquely backward, 

 with a slightly convex outline; postero-basal extremity rather narrowly rounded; 

 hinge comparatively short, and standing at an angle of about 60° to 90° from the 

 slope of the anterior margin : beaks oblique, rather convex, but narrow, pointed, nearly 

 or quite terminal, rising little above the hinge. Surface ornamented by distinct con- 

 centric undulations, which are subangular, nearly simple, and quite regular on some 

 specimens, but more rounded and irregular on others. Between these undulations 

 traces of finer marks of growth are also sometimes seen. 



Length of largest specimen about 3 inches ; breadth of same near 1.50 inches. 



