446 (1I':()L0(1Y OF THE BLACK HILLS. 



consisting of two divisions, the first cordiform and the second simple and 

 rounded. Third sinus composed of two parts, both sHghtly flattened on 

 their upper surface. Fourth sinus simple, with a slight indentation at the 

 middle. The sinuses are all broad and the lobes very narrow. Siphuncle 

 not observed. 



This species is a well marked and easily distinguished form am^ng the 

 fossils of this region, and appears to be quite abundant at some localities. 

 It is very closely related to S. cequalis Sow., and not readily distinguishable 

 from it, except in the form of the aperture, which in that one seems to be 

 bordered by a thickened margin, while in this one it is contracted to about 

 two-thirds the size of the shell, with the edge rather thin, or thickened very 

 slightly only on the inner surface. The shell is quite variable in size at 

 different localities, but appears to retain the full, ventricose form of the 

 volutions and other specific features to quite a remarkable degree. 



Formation and locality. — In Lower Cretaceous shales at the outer edge 

 of Camp Jenney, east fork of Beaver Creek, Black Hills, Wyoming. 



SCAPHITES WYOMINGENSIS. 



Plate 13, figs. 5-7. 



Scaphites icarreni var. loyomingemis M. & H., PaL U. S. Geol. Surv. Terr., p. 421, figs. 

 CI, 02. 



The shells of this species closely resemble those of S. warreni M, & 

 H. in many of their features, but differ very materially in the general 

 form and proportion, as seen in the specimens from the Black Hills locali- 

 ties. They are always much smaller, and the volutions are laterally com- 

 pressed, so that their relative diameters are scarcely more than as two to 

 three, as seen on the involute parts, but widen rapidly on the deflected and 

 recurved parts, so that near the aperture the lateral diameter is greater 

 than the dorso-ventral. The deflected portion is also always proportion- 

 ally longer than in that one, the surface marking very much finer, and 

 those on the straight portions have a more strongly forward curvature. 

 The septa have the same general character as in S. warreni, but the digita- 

 tions of the lobes are smaller and less distinct, presenting about the same 

 features in the extreme adult shell as is possessed by the septa of the rep- 



