Logan.] The Invertebrates, Benton Group. 451 



pressed, thin and fragile ; anterior side forming a slightly 

 convex curve from the beaks obliquely downward and back- 

 ward ; postero-basal extremity rather narrowly rounded ; pos- 

 tero-dorsal margin very oblique, compressed, nearly straight, 

 or sometimes a little convex in outline below the middle, and 

 slightly concave above ; cardinal border short, straight, com- 

 pressed, and forming an angle of about forty-five degrees with 

 the longest diameter of the shell ; beaks terminal, rather small, 

 nearly equal, obtusely pointed, rising little above the hinge, 

 and not much curved. Surface ornamented by more or less 

 regular, concentric undulations, and smaller marks of growth. 

 Greatest length, four inches ; breadth at right angles to the 

 longest diameter, about two inches ; convexity of the two 

 valves, about eight-tenths inch." 



To the above description Stanton added : " The name Inocera- 

 m us a viculoides was applied by Meek and Hay den to a variety with 

 a longer hinge line, greater convexity, and more prominent beak 

 of the left valve, and with the dorsal region more alate than is 

 usual in the species. After studying larger collections Professor 

 Meek found that there were many gradations between this and 

 the typical form, and he therefore treated it as only a variety. 

 Like all species of the genus, it is subject to considerable varia- 

 tion in form, yet it is always easily recognized by its obliquely 

 elongate outline and by the character of the surface markings. 



' ' It is unfortunate that the law of priority compels us to drop 

 the name that has for many years been applied to this species 

 by all American writers who have referred to it, and it is the 

 more unfortunate because the species is so well known under that 

 name as the most abundant characteristic fossil of the Colorado 

 formation. There is no doubt, however, that the American 

 fossil belongs to the species to which European paleontologists 

 now apply the earliest name Inoceramus labiatus." 



This fossil is extremely abundant in the Fort Benton lime- 

 stone of Kansas. In one horizon 08 of the limestone group the 

 rock is composed almost entirely of Inocerami. This horizon is 



68. The Inoceramus horizon; see Upi>er Cretaceous of Kansas, Logan, Kans. Univ. Greol. Surv., 

 toI. II, pp. 216, 217. 



