185G.] 



71 



around Avhich on the outer wborl, they swell out into a row of prominent trans- 

 versely elongated nodes or ridges, while the intei mediate ones die out, or coalesce 

 Avith the others at various distances across from the periphery. 



Septa profoundly lobed, and exceedingly complicated. All the margins of the 

 branches of the lobes, sharply, and those of the saddles obtusely, digitate. 

 Dorsal lobe ornamented at the extremity with four principal branches, the two 

 terminal of which are larger than the others, and again divided into two branch- 

 lets. Dorsal saddle much larger than the superior lateral lobe, incqually divided 

 at the summit by the slender digitate auxiliary lobe into two branches, that on 

 the dorsal side being much larger than the other, and again once or twice dyeply 

 divided. kSuperior lateral lobe much smaller than the dorsal saddle, and having 

 four principal divisions, the two terminal of which are greatly larger than the 

 others, and each again divided into two branchlets, of which the two lateral are 

 much smaller than the others. Superior lateral saddle a little smaller than the 

 superior lateral lobe, deeply divided at the summit into two nearly equal 

 branches, each of the divisions being again divided into two or three parts. 

 Inferior lateral lobe small and slender, having four or five alternating branches. 

 The succeeding lobes are very small and simply bifid or trifid at the extremity. 



It is exceedingly difficult, if not impossible, from our imi)crfect specimens, to 

 determine definitely whether this is Scaj^hile or an Ammonite, though we are in- 

 clined, in consequence of its large size, to think it must be the latter. Our de- 

 scription is made out from a young shell measuring four and a half inches across 

 the disc, while \y& have fragments of other individuals which must have been 

 at least four times as large ; hence we infer, in adult shells of large size, the 

 lobes of the septa may have been even more complicated than those of the spe- 

 cimen investigated hj us. 



From the same bed we have a large distorted specimen, apparently of the 

 same species, which is less compressed and has stronger costae. It also appears 

 to want the row of nodes round the umbilicus. As far as we have been able to 

 see its septa, they appear to be identical with those of the above species ; con- 

 sequently we are disposed, at present, to regard it as only a variety of the same. 

 It is possible, however, a careful comparison of better specimens may prove 

 them to be distinct ; if so, we would propose for it the specific name of ampins. 



This species is named after Prof James Hall, of Albany, N. Y. 



Locality and position. Yellow-stone River, one hundred and fifty miles above 

 the mouth, and one hundred and fifty miles above Milk River, No. 4 of series. 



Ancvloceras? Nebeascensis. Of this species we have but a fragment, .about 

 two inches in length. It makes a short spiral curve like Helioccras (D'Orb.) and 

 is ornamented with small (bifurcating?) annular costje, more distinct on the 

 ventral than dorsal side. The specimen is too imperfect to show the details of 

 the lobes, though we can see they are very complicated, and sharply digitate. 

 Section circular, diameter .90 inch. 



This and the following species would not go into the genus Ancyloceras, as 

 defined by D'Orbigny, but appear to be closely related to foriBS, so referred by 

 Pictet and others. 



Locality. Iquor creek, north fork, Cheyenne. Position. No. 4 of the series. 



Ancyloceras? Cheyenensis. The only specimen of this species we have 

 seen, is a.section of the outer chamber, about two and a half inches long. It 

 makes a broad spiral curve, and is ornamented by prominent rounded annular 

 costsR, which encircle the shell very obliquely, and are smaller and more ap- 

 proximate on the inner side of the curve, than without. Costre having two 

 prominent nodes, at which point iAiQj sometimes bifurcate ; the nodes being so 

 arranged as to form two parallel rows up and down the dorso-lateral portion of 

 the shell. Section circular, diameter 2.40 inches. 



The above species resemWes somewhat Ancyloceras? Nicolletii of Hall and 

 Meek (Vol. 5, new series. Trans. Am. Acad. Arts and Sciences, Boston,) but has 

 much larger and more prominent costre, which pass less obliquely round the shell, 

 and do not bifurcate so frequently, while the nodes are larger, and the curve of the 



