Maryland Geological Survey 379 



Description. — " Discoid ; umbilicus deep, outer volution covering one- 

 half to two-thirds of the next one within ; volutions five or more, ventri- 

 cose, nearly twice as wide as high ; ornamented on the ventral edge by 

 about ten or twelve transverse nodes, slightly elevated, and extending out- 

 wards in bifurcating annulations, which cross the back of the shell, unit- 

 ing again on the oposite side in the same manner. Between these annu- 

 lations are often other intermediate ones, which are equally prominent on 

 the back of the shell, and die out on the ventral edge. 



" These nodes, although existing in the young shell, are scarcely pro- 

 longed into annulating ridges, and the back of the shell is smooth, or 

 marked only by the ordinary lines of growth. 



" In a young specimen 0.64 in. in diameter, aperture 0.34 in. high, and 

 0.49 in. wide, septa formed of three symmetrical lobes on each side. Dorsal 

 lobe as deep as the dorsal saddle, but wider, deeply divided at its 

 extremity, and ornamented by two large terminal branches, the outer sides 

 of which are deeply sinuate, a large lateral oblique branch midway between 

 the apex and base of the lobe. Dorsal saddle deeply divided at the 

 extremity into two unequal parts; the upper one again deeply bifurcate, 

 divisions digitate at the extremities ; ventral division bifid at the tip ; a 

 small branch on each side opposite the extremity of the auxiliary lobe. 

 Superior lateral lobe extremely contracted in the middle by the lateral 

 branches of the saddle ; divided towards its extremity into three unequal 

 branches, the terminal one trifid at its extremity, the lateral ones scarcely 

 digitate ; two smaller lateral branches towards the base. Lateral saddle 

 in form like the dorsal saddle, with the ventral division larger and 

 bipartite, corresponding to the dorsal division of the other. Inferior 

 lateral lobe shorter than the superior ; contracted near the middle, divided 

 into three subequal branches, the lateral ones irregularly digitate, and the 

 terminal one trifid. Ventral saddle oblique, divided by the auxiliary lobe 

 into two branches, which are again bifurcate, with the extremities obtusely 

 bifid. Ventral lobe much smaller and shorter than the inferior lateral 

 lobe, subequally tripartite, with the divisions subdigitate. A small bilobed 

 saddle on the ventral side of the last lobe." — Hall and Meek, 1855. 



