CRETACEOUS FOSSILS. 83 



the suture and merge into the surface below the point of greatest 

 convexity of the whorl ; these are crossed by a few small, but dis- 

 tinct, revolving ribs. Where the longitudinal ribs approach the 

 perpendicular, they show, in one or two cases on the specimen, 

 a tendency to form an obtuse angle. Between these ribs the sur- 

 face is broadly and regularly concave, the interspaces being a 

 little wider than the ribs themselves. 



Figure, natural size. 



Locality: A single specimen found by myself at Bull's Head Point, northeast of 

 Martinez. 



F. Mathewsonii, n. s. 



PI. 18, Fig. 33. 



Shell fusiform, spire turreted; whorls seven, angular. Aper- 

 ture about as long as the spire, narrow ; inner lip slightly in- 

 crusted, outer lip simple. Body whorl biangular; the upper 

 angle acute and more prominent than the lower, which is obtuse. 

 Surface marked by alternating ribs, some of which are linear, 

 while others are quite broad. 



Figure, natural size of the largest specimen. 



Locality: Martinez (Div. A.), collected by Mr. Mathewson, to whom the Sur- 

 vey is indebted for a number of fine specimens. I have also found it at Clayton, 

 in a stratum of brown sandstone, overlying the coal ; and at Cochran's, six miles 

 east of Mount Diablo, in Div. B. Imperfect specimens from Curry's, south side 

 of Mount Diablo. 



F. Averillii, 11. S. 



PL 18, Fig. 34. 



Shell slender, fusiform, spire high, acute; whorls seven, sloping 

 on the upper surface, rounded on the side, except the body whorl, 

 which is obtusely angulated. Lower part of the body whorl 

 unknown. Suture impressed, distinct. Surface marked by 

 slightly oblique, rounded ribs, which commence just below the 

 suture, and, after crossing the shoulder of the whorl, pass about 

 an equal distance below it. These are crossed by a few revolving 



