FROM THE CEXTACEOrS FORMATION OF NEBRASKA. 397 



dissimilar in details) ; extremities digitate, the one on the right having two, and that on 

 the left three divisions ; sides u-regularly sinuous ; dorsal saddle as long but not as vdde 

 as the dorsal lobe, bipartite at the extremity, the right branch digitate and the left 

 subdivided ; superior lateral lobe longer and more diverging than the dorsal lobe or 

 the dorsal saddle, deeply divided into two principal branches, each of which is again 

 subdivided, with numerous shallow, irregular sinuosities along the margin. Lateral 

 saddle very much contracted near the middle, shorter than the dorsal saddle, deeply 

 divided into two branches, which are digitate. Inferior lateral lobe as long as the 

 superior lateral lobe, but narrower, deeply divided into two branches, each of which 

 is again divided, the divisions digitate. Ventral saddle shorter than the lateral saddle, 

 oblique, divided into three lobes at top with smaller ones below. Ventral lobe little 

 more than half as long as the inferior lateral lobe ; bifid at the apex, and with three 

 or four small divisions on each side. 



This species resembles in its external characters the H. torquatus of Morton, 

 {Synopsis, PL XX. fig. 4,) but the annulations are relatively closer together and less 

 acute than those described by Dr. Morton, and differ in being sometimes distinctly 

 nodose and bifurcating. The fragment possessed by us makes a shorter curve than the 

 figure cited above. In addition to these differences, we may observe that our shell 

 makes a broader or more circular ciu've than is usual in the species of Hamites, and 

 moreover appears not to cuiTe precisely in the same plane, resembling in this respect 

 the genus Helioceras of D'Orbigny, while the septa correspond with those of 

 Hamites. 



Locality and Position. — Xear Eed Cedar Island, thu'ty-five miles below Fort Pierre, 

 in division No. 4 of Section. 



AnCTLOCERAS ■? NiCOLLETII, n. sp. 

 Plate n^. Fig. 4. 



The fragment in our collection appears to be a part of the outer chamber, including 

 the abrupt curved portion, of a shell of this genus. 



Section oval or sub-circular, shell thin, abruptly curved towards the aperture, surface 

 marked by distinct annular costte, which encircle the shell in a very oblique du-ection, 

 and become obsolete on the ventral side of the curve, and very irregular in size and 

 distance from each other upon the lateral portions of the shell, often bifurcating once 

 or twice, with sometimes small nodes at the bifurcation, becoming more prominent 

 and equidistant upon the dorsum. 



