INVERTEBRATES. 387 



versely than from the dorsal to the ventral side, and increases 

 rather gradually in size, from the smaller to the larger end, 

 being evidently part of a discoid shell, with an umbilicus about 

 equaling the transverse diameter of the outer whorl. On the 

 dorsum it is nearly flat, or but slightly convex, and the sides 

 are a little concave with an outward slope, the greatest con- 

 vexity of the whorls being at the margin of the umbilicus. The 

 ventro-lateral margins are obliquely flattened so as to form an 

 abrupt slope into the umbilicus, leaving a subangular promi- 

 nence around the margin of the umbilicus. The ventral side 

 is moderately concave along the middle, for the reception of 

 the inner whorls, each of which is probably about one-third 

 hidden. On each dorso-lateral angle there is a series of rather 

 low nodes, about twenty-three to twenty-four of which proba- 

 bly existed on each entire whorl. 



A transverse section of the whorls is nearly quadrangular 

 in outline, if we regard the small ventral concavity, and the 

 two sloping ventro-lateral margins together as one side. The 

 septa are moderately concave, and arch gracefully backwards 

 on each side, and in the ventral depression ; while they make 

 a less distinct curve in the same direction in crossing the 

 periphery or outer side. The siphuncle is small, and located a 

 little nearer the outer than the inner side of the whorls. 

 Aperture and surface markings unknown. Length, or greatest 

 diameter, as inferred from the curve, about 2 inches ; height, 

 about 1.45 inches; breadth near the aperture, 0.88 inch. 



This species bears some relations to N~. occidentalis, Swallow, 1858(=iV. 

 quadrangulus, McChesney, 1860), but has more slender whorls, and its dorsum 

 differs in being moderately convex and smooth along the middle, instead of con- 

 cave and provided with two rows of nodes. Its dorso-lateral nodes are likewise 

 less prominent, and its ventro-lateral angles differ in being destitute of any 

 traces of nodes. The whorls of our shell are also more deeply embracing than 

 those of the species described by Prof. Swallow. The form published by Prof. 

 McChesney under the name of 2V. nodocarinatus, is also only a variety of the 

 iVi occidentalis. 



Our shell is more nearly like a form referred by Murchison, deVerneuil and 



