CEETACEOUS FOSSILS. 451 



served. The outer extremity of the specimen retains a part of the deflected 

 portion, which is bent downward as well as outward, and is septate nearly to 

 the end. The species appears to be related to H. f nebracensis M. & H. 

 (Paleontology of the United States Geological Survey of the Territories, 

 p. 480, PI. 22, Fig. 1, a, b, c), but differs, however, in the more rapidly- 

 increasing volutions, in the disconnected whorls, simple costae (i. e., not 

 bifurcating), in the position of the siphuncle, and in the details of the lobes 

 and sinuses. 



Formation and locality. — In limestones of the Fort Pierre' Group, on the 

 west side of Beaver Creek, Black Hills. 



HETEEOCEEAS % NEBEASOES'SE. 



Plate 15, fig. 6, and Plate 14, fig. 9. 



Ancyloceras ? nebrascense M. & H., Proc. Acad. Nat. Sci. Phil., vol. viii, p. 71. 

 Turrilites nebrascense M. & H., ibid., p. 280. 



Melicoceras f nebrascense Meek, Smithsonian Check Llist Invert. Foss., p. 25. 

 Heteroceras ? nebrascense Meek, Pal. TL S. Geol. Surv. Terr., p. 480, PI. 22, fig. 4. 



Shell moderately large and robust, with a low, rapidly- contracting, 

 dextrally-coiled spire, having an apicial angle of about 50°, and com- 

 posed of a small number of rapidly-increasing volutions, which are in close 

 contact with each other, as far as observed in the example figured, and 

 coiled so as to leave an umbilical opening of large size in the upper 

 portion of the spire, which apparently increases but little in diameter with 

 the increased growth of the shell. Transverse section of the volutions cir- 

 cular or nearly so. Surface of the shell ornamented by strong, subangu- 

 lar, transverse ridges or costa?, which pass entirely around the shell and are 

 divided by concave interspaces. The costae on the smaller volution of the 

 specimen are often duplicate, and cross the face of the volution with a strong 

 forward direction in passing from above to the lower side, but are directed 

 strongly backward from within the umbilicus on the upper surface. On 

 the larger volution the costse are usually simple, but sometimes bifurcate, 

 and pass more directly across the shell. The costse are ornamented by two 

 irregular rows of strong, rounded nodes on the older parts, situated one near 

 the periphery and the other just above the base of the volution. 



