41 



> 



spire, below which point the shell is deflected to an unknown extent. 

 Transverse section of the shell circular, or nearly so. Umbilicus very 

 wide in the upper part of the spire, but scarcely increasing in diameter 

 with the increased growth of the shell above the deflected portion, the 

 increased diameter of the tube about equaling the increased diameter 

 of the whorl. 



Surface of the shell ornamented by low, subangular, transverse ridges 

 or costa, which pass entirely around the shell and are separated by 

 wider concave interspaces ; also by two longitudinal rows of obliquely 

 rounded nodes, the upper one of which is placed at, or just below, the 

 periphery, and the other at about one-eighth of the circumference of 

 the tube below the first, and on the line of the same ridge with it. 

 Transverse costa arranged in sets of three 5 two of each set coalescing 

 to form the oblique nodes, the third one passing around the tube, without 

 interruption, midway between the two adjacent pairs of nodes. The 

 direction of the costa is strongly backward on the upper inner surface 

 of the volution, then recurving and passing obliquely forward in cross- 

 ing the outer face of the shell from above to the base, and also within 

 the umbilicus. Siphuncle small, marginal, situated as far above the 

 upper line of nodes as the distance between the two lines. 



Septa approximate, the extremities of the lobes of one slightly inter- 

 fering with those of the saddles of the next adjacent, but not interlock- 

 ing ; the space occupied by the convolutions of the lobes and sinuses of 

 a septum is equal to three-fifths of the diameter of the tube at the 

 position of the septum measured ; the ramifications of the lobes are 

 sharply angular and pointed. The siphonal lobe is longer than wide,, 

 deeply divided at the extremity into two rather long, compound digitate 

 processes, and a short median bifid process. First lateral lobe very 

 deeply and unequally divided and the branches widely spreading,, 

 and deeply serrate-digitate. Second lateral lobe very much smaller than 

 the first and less spreading. Antisiphonal lobe single, longer than wide, 

 deeply digitate on the side and divided into four small, unequal digita- 

 tions at the extremity. Sinuses large, spreading, and deeply cleft by 

 auxiliary or secondary lobes. 



The type specimen of the species is imperfect, but preserves one and 

 one-third volutions ; the volutions are entirely disconnected and increase 

 rapidly in size, while the umbilicus retains the same diameter, the upper 

 volutions appearing to have been not more closely coiled than those 

 preserved. 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., Pal. U. S. Geol. Surv. Territ., p. 480, pi. 22, fig. 1, 

 a, &, o, but differs, however, in the more rapidly increasing volutions ; 

 in the disconnected whorls ; simple costa (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, southwest Black Hills. 



