CRETACEOUS FOSSILS. 89 



N". PERFORATA, n. 8. 

 PL 18, Fig. 39. 



SMALL, robust; whorls five, very convex, suture deep; first two 

 wliorls smooth or finely cancellate, remainder ornamented by 

 large, oblique ribs, nearly as high as wide, starting at the suture, 

 aiid extending nearly the whole width of the whorl, becoming 

 obsolete at their lower ends. These are crossed by numerous 

 sharply defined, linear, revolving ribs, which cover the whole 

 surface, and occasionally, though rarely, alternate in size. Aper 

 ture wide, rounded. Outer lip acute on the edge, inner surface 

 smooth (? judging from the cast); columella incrusted, pierced 

 anteriorly by a minute, shallow, umbilical depression; no trace 

 of a sinus anteriorly. 



The usual size of the specimens is about .4 inch ; the largest is .55 inch. 

 Locality: North fork of Cottonwood Creek (Div. A.); not rare. 



? N. SUPRAPLICATA, n. 8. 

 PL 18, Fig. 40. 



SHELL small, fusiform; whorls five or more, regularly convex; 

 suture well marked; spine nearly as long as the mouth. Surface 

 marked by a number of small longitudinal folds on the upper 

 half of the whorls, commencing at the suture ; remainder of the 

 body volution covered by distinct revolving ribs of about equal 

 size throughout. Canal slightly curved. Aperture unknown. 



Length, about .55 inch. 



This shell is of about the same size, and nearly the shape of Nassa cretacea ; but, 

 even in fragments, it can be distinguished by the higher and more slender spire, 

 and the peculiarity of the surface-markings. 



Localities: San Diego, collected by Dr. Cooper; and (?) Clayton, Contra Costa 

 County (casts). 



PAL. VOL. I. 12 



