90 PALAEONTOLOGY OF CALIFORNIA. 



N. HoFFMANNII, n. S. 



PL 18, Fig. 41. 



Short, robust, shell thick; whorls five or six, convex; suture 

 linear, marked below by a slight carina on the upper edge of 

 the succeeding whorl. Surface ornamented by oblique, slightly 

 sinuous ribs, which do not extend to the suture above, and be- 

 come obsolete just below the line of greatest convexity of the 

 whorl. These are crossed by a few revolving ribs, which dis- 

 appear on the lower third of the whorl. Besides these, there are 

 irregular, and, in some cases, prominent lines of growth. Aper- 

 ture wide ; columellar lip slightly incrusted; canal short, not emar- 

 ginate anteriorly. 



Figure, natural size. 



Locality: North fork of Cottonwood Creek (Div. A.). Named in honor of Mr. 

 Hoffmann, the topographer of the Geological Survey. 



N. GRACILIS, 11. S, 

 PL 18, Fig. 42. 



Slender, fusiform; shell very thick; spire small, slender, not 

 as long as the mouth; whorls convex. Aperture narrow, rounded 

 posteriorly; canal somewhat elongated, slightly curved. Surface 

 marked by small, regular, angular, revolving ribs, crossed by 

 longitudinal undulations. 



The only specimen I have seen is injured by the external layer 

 of the shell having been broken off with the matrix, leaving only 

 undulations in the place of the ribs. The internal surfaces of 

 the shell in the aperture seem to exhibit the same ribs as the sur- 

 face, although the substance of the shell itself is unusually thick. 



Length of the fragment (having lost the upper one or two 

 whorls), .8 inch. 



Locality: Bull's Head Point, northeast of Martinez (Div. B.). Collected by Mr. 

 Mathewson. 



