37 



GASTEROPODA. 



FUSUS CHEYENNENSIS, n. 8p. 



Plate 12, fig. 9. 



Shell small, spire slender and elevated, the number of volutions un- 

 known, but probably six or more, strongly rounded, the last one some- 

 what ventricose above the middle but attenuate below ; aperture semi- 

 ovate, being rather straightened on the inner side and slightly produced 

 below. Volutions crossed by numerous vertical folds or plica?, which 

 are very slightly bent backward in their course across the volution. 

 Surface of the shell unknown. 



The specimen from which the description is drawn is an internal cast, 

 and therefore the external characters cannot be given in detail. The 

 species is, however, so entirely distinct from any of the forms known 

 from this region, that there is no fear of its being confounded with any 

 of them. 



Formation and locality. In the gray shales near the upper part of the 

 Fort Pierre group. On the Cheyenne River, near Rapid Creek, Black 

 Hills, Dakota. 



APORRHAI^ MEEKI, n. sp. 



Plate 12, fig. 5. 



Shell of moderate size, with a low, very obtusely pointed spire, which 

 is composed of only three ventricose or rounded volutions, exclusive of 

 the apertural expansion, and which rapidly increase in size ; apical angle 

 nearly eighty degrees. Volutions marked by numerous sharply elevated 

 revolving lines, with concave interspaces both above and below the 

 middle. Outer lip expanded, and extended into two diverging carinated 

 digitations of an undetermined length, which are deeply grooved on the 

 inner face, the upper one being directed slightly backward toward the 

 spire, and the other one slightly downward and more strongly forward 

 in the direction of the coil of the shell ; anterior beak, judging from the 

 part remaining, moderately long and stout ; posterior canal extending 

 along the spine to the summit, where it appears to have become free 

 and deflected ; callous slight(?), coating the upper volutions over a part 

 of their extent. 



This species differs from any previously described form of this group, 

 in the short obtuse spire, combined with the two digitations of the outer 

 lip, and the posterior canal which extends to the summit of the spire. 



Formation and locality. In limestone of the Fort Pierre group, at the 

 top of the gray shales of this formation. On the Cheyenne River, near 

 Rapid Creek, Black Hills, Dakota. 



