CRETACEOUS FOSSILS. 153 



NEtERA, Gray. 



N". DOLABRJEFORMIS, 11. 8. 

 PI. -2-2, Fig. 125. 



Shell small, convex ; beaks central, strongly incurved, nearly 

 touching; anterior end suddenly narrowed, produced; extremity 

 unknown ; posterior end narrowly rounded ; base broadly sinuated. 

 Surface marked, except on the anterior end, by moderately large, 

 rounded ribs, somewhat variable in size and closely placed. 



Length, .45 inch; width, .33 inch. 



Locality: East of Martinez (Division B.). 



MACTRA, Linn., Lam. 



M. ASHBURNERII, 11. s. 

 PI. 22, Fig. 127. 



Shell moderate in size, subtrigonal ; base broadly and regu- 

 larly convex; beaks central, slightly inclined forwards; posterior 

 cardinal margin sloping, straight, or slightly convex; anterior 

 faintly excavated; some specimens show an umbonal angle 

 well marked, while in others it is nearly or entirely obsolete. 

 Surface variable ; specimens from some localities showing a 

 large number of regular, nearly uniform, rounded, concentric 

 ribs ; while those found at other places have these ribs few, en- 

 tirely absent, or only represented by tine lines of growth. 



Figure, average size. Some few specimens have been found a third larger. 



Localities: Pence's Ranch, Butte County, Mr. Ashburner; Chico Creek; Texas 

 Flat, Placer County; near Martinez; Tuscan Springs, Tehama County ; Orestimba 

 Canon, Stanislaus County; Benicia; San Luis Gonzaga Ranch, Pacheco's Pass; 

 in Division A. ; and in Division B., at Martinez; Marsh's, southeast of Mount 

 Diablo ; Alizos Creek, near Fort Tejon, &c. 



This is one of the most common fossils in the State. 



PAL. VOL. I. — 20 



