4 PALAEONTOLOGY OF CALIFORNIA. 



or less regularly alternating in size; these ribs are crossed by 

 strong lines of growth, so as to present in some specimens an ap- 

 proach to a regular reticulation. Body whorl three-fourths of 

 the whole length of the shell, broadly and regularly convex in 

 the middle, with usually a revolving depression just below the 

 suture ; sometimes this groove or depression is replaced by a flat 

 space. Mouth long and narrow; inner lip slightly incrusted; 

 outer lip unknown; canal straight. 



Figure, natural size. 



Locality and position : From the Miocene of Arroyo San Antonio, near Tomales 

 Bay. 



The specimens are all preserved in a very hard gray sandstone, and I have 

 been unable to expose the outer lip, so as to ascertain whether the characters exist 

 on which the authors have mainly depended in instituting the genus. The form 

 of the shell, however, and all the other characters are so nearly in accordance 

 with their type, that I have ventured to place the species under their generic 

 name provisionally. 



CLAVELLA, Swains. 



C. GRAVIDA, 11. S. 

 PI. 1, Fig. 6. 



Shell short, robust; spire moderately elevated, whorls five, 

 suture channelled; body whorl bordered above by a strongly 

 marked rim, adjoining the suture, and which extends to the 

 upper whorls, though less distinctly marked ; below this baud is 

 a slight depression of variable depth, and from that the volution 

 swells rapidly. Surface marked by two or three rows of nodes 

 on the middle of the whorl, and by fine revolving lines. Aper- 

 ture broad in the middle, narrowing in advance; canal moderate, 

 slightly twisted; inner lip slightly incrusted. 



Figure, natural size. 



Localities: From the Miocene; abundant south of Martinez, where it was col- 

 lected by Dr. Fish and Mr. Mathewson. Also figured in the Pacific Railroad 



