[NVERTEBRATE PALEONTOLOGY. 51 



would evidently be correctly restored it' made to conform much more 

 nearly to the outline of our specimens. This view is also confirmed by other 

 more nearly entire specimens from Alabama, which agree almost exactly with 

 our shell. Professor Tuomey proposed the name Inoccramus gibbus for this 

 form; but as it was evidently regarded by Dr. Morton as the typical form of 

 his species, which he describes as " obliquely elliptical," while he first refers 

 to it in connection with the name, we cannot do otherwise than retain his 

 name for it, whether we view it as a distinct species, or regard his specimens 

 as representing two marked varieties. I should remark, however, that the 

 original specimen of his other form represented by fig. 11 of his pi. xiii 

 is tar from correct, its beaks being represented too prominent, and too far 

 back. The curves of its undulations are also incorrectly represented ; and 

 the posterior margins ought not to have been drawn as if the specimen shows 

 its outline entire, because this margin is broken, and may have presented a 

 very different outline from his figure as engraved. (See our cut No. 3, of last 

 page, from his original specimen.) 



Although by no means satisfied that this shell is identical with Mantell's 

 I. Cripsii, I have concluded to place it provisionally as a variety of that spe- 

 cies, in deference to the opinions of European palaeontologists, who seem to 

 refer all such forms to Mantell's species. Compared with the last, it will be 

 seen to differ in its more prominent and terminal beaks, longer hinge-line, 

 and rounded instead of oblicpiely-truncated posterior margin, while its valves 

 are also more convex in the umbonal region. In all of these characters, how- 

 ever, excepting its more prominent beaks and more retreating anterior ven- 

 tral margin, it conforms more nearly to the general idea of Z Cripsii than the 

 last-described form does. 



Locality and position. — Yellowstone River, one hundred and fifty miles 

 above its mouth, in Montana ; from the Fort Pierre group of the Upper Mis- 

 souri Cretaceous. 



iDOCtra in us convex us, H. & M. 



Plate 12. figs. 5, a, b. 

 Tnoceramus convacus, Hall and Meek (1854), Mem. Am. Acad. Arts and Sci., V (n.s.), 38G, pi. 2, fig. 2, a, h. 



Shell ovate, very convex, height a little more than three-fourths the 

 length; beaks prominent: hinge-line long and straight, forming an angle 





