1856.] 



281 



Gen. ANCYLOCERAS. ^ 



A? NicoLETTi, Hall and Meek, Mem. Am. Ac. Arts & Sc. Host. vol. 5, new 



ser. p. 397 



A. MoRTONi, Hall and Meek, Mem. Acad. Arts & Sc. Bost. rol. 5, new ser. 



p. 396 (see corrections at end of that memoir) 



Gen. BACULITES. 

 II B. ovATtJS, Say, Jour. Ac. Nat. Sc. Phila. vol. 1, pi. 5, fig. 5 and 6 



B. COMPRESSUS, Say, Am. Jour. Sc. vol. 11, p. 41 



B. GRANDis, Hall & Meek, Mem. Am. Ac. Arts & Sc. Bost. vol. 5, n. s. p. 402 



Gen. SGAPHITES. 

 II S. CoNRADi,* Morton, sp 



Ammonites Conradi, Morton, 1834, Synopsis Org. Remains, p. 39 



A. JVebrascensis, Owen, Report Iowa, Wis. and Min. tab. 8, fig. 3 and 

 3a, tab. 8a, fig. 2 



A. Nebrascensis? Owen, Report Iowa, Wis. and Min. tab. 8, fig. 2 



A. Moreauensis, Ow^n, " " " " fig. 7 



A. Cheyennensis, Owen, " " " tab. 7, fig. 2 



S. Mandanensis,! Morton, sp 



Ammonites 3Iandanensis, Morton, Jour. Acad. N. S. Phila. v. 8, p. x. fig. 2 



?A. ahyssinus, Morton, " " " " " 



A. 3Iandanensis ? Owen, Report Iowa, Wise, and Minn., tab. 7, fig. 5 

 S. NicoLLETii, Morton, sp. 1841, Journ. Acad. N. S. Philad. vol. 8, pi. 10, fig. 3 



S. comprimus, Owen, 1852, Report Iowa, Wise, and Minn., tab. 7, fig. 5 



Ammonites Nicolletii, Morton, Jour. Acad. N. S. Phila. vol. 8, pi. x. fig. 3 

 S. NODOsus Owen, (not of others,) Rep. Iowa, Min. & Wis. tab. 8, fig. 4 and 4 



Formations in 

 ascending ordei-. 



4 |5 



* Of this truly protean species we have a fine collection of beautiful specimens from 

 the same locality and position as those investigated by Dr. Owen. These we find agree 

 in all respects with his figures, and only differ from his descriptions in always exhibit- 

 ing, when the matrix is cleared out from the umbilicus, six or seven volutions, instead 

 of one and a half to three and a half. A critical comparison of our specimens, with 

 Dr. Owen's figures and Dr. Morton's original specimens in the cabinet of the Academv 

 at Philadelphia, as well as with others from Alabama, loaned us by Prof. Winchell, 

 leads us unavoidably to the conclusion, that they all belong to one exceedingly variable 

 species, in which opinion Mr. Conrad, who has looked over our specimens, concurs 

 with us. A. Nebrascensis, A. Moi-eauensis, and A. Cheyennensis of Owen, are the inner 

 volutions of one strongly marked variety having a larger umbilicus, narrower volutions 

 and stronger costse. It is diflficult to believe this is not a distinct species, yet after 

 a very cai-eful comparison, we cannot see any difference between the septa of shells 

 having these characters, and those of well marked specimens of S. Conradi. 



f We have perfect specimens of this species, which prove it to be a true Scaphite. 

 Like S. Conradi, it invai'iably shows, when the matrix is removed from the umbilicus, 

 about seven volutions. When divested of the outer whorls, it is so nearly like Dr. 

 Morton's figures of his Ammonites ahyssinus, that we cannot see the slightest difference ; 

 the perforate character of the umbilicus in the specimen figured by him, being proba- 

 bly due to accident. The lobes of the septa of this species are very nearly like those 

 of S. comprimus of Owen, yet we have seen no intermediate gradations of extei-ual form 

 connecting those two, like those between the different varieties of & Conradi. We find 

 it exceedingly diflficult to define limits between species amongst these Nebraska 

 Scaphites. The position and relative size of nodes and costa3, as well as the more or 

 less compressed form of the shell and relative size of the umbilicus, are not, within a 

 considerable range of limits, characters that can always be relied upon. One of our 

 specimens of S. nodosus, (Owen) for example has near the dorso-lateral margin of one 

 side, the usual row of nodes, and none at all on the other. 



