CRETACEOUS FOSSILS. 171 



of the upper margin of the whorl, and abut against a strongly 

 marked revolving rib bordering the lower angle; these are crossed 

 by six or seven smaller revolving elevated lines; under surface 

 marked by numerous, minute, revolving striae. Aperture sub- 

 quadrate; inner lip straight, slightly oblique and thickened. 



Length, .16 inch ; width, .18 inch. 



This species is known by but a single specimen from the Cbico Group of Texas 

 Flat, Placer County. It is not improbably a young shell, though it already pos- 

 sesses four volutions. It has so well-marked a series of characters that I have 

 ventured to describe it, since it cannot be confounded with any known species. 



ATAPHRUS, N. Gen. 



Shell thick, flattened subglobose. Surface smooth. Aperture 

 subovate, oblique; outer lip simple, inner lip thick, rounded, 

 uniting with the outer lip by a regular curve; umbilicus entirely 

 hidden. 



The present genus seems to occupy an intermediate position between the recent -".* 



genera Oxystele, Phil., and Photinula, H. and A. Adams. Prom the former it 

 differs in having a rounded columella, instead of flattened ; while from the latter, 

 it can be distinguished by its smooth surface and the junction between the labrum 

 and labium being by a regular curve in front, instead of the columella terminating 

 in a point near the external edge, as in Photinula. 



A. CRASSUS, n. S. 

 PI. 28, Fig. 54. 



Shell small, thick, flattened subglobose, spire low ; whorls 

 four, rounded, revolving a little obliquely; body whorl slightly 

 flattened below. Surface marked only by lines of growth. Aper- 

 ture oblique, subcircular, columellar lip thick and rounded ; um- 

 bilical region covered by a smooth callus, which merges insensibly 

 into the general surface. 



Length, .18 inch ; width, .28 inch. 



Rare in tho Martinez Group (?) at Martinez. Specimens were sent me by Mr. 

 Mathewson, but not so labelled that I can determine their horizon, and they are 

 so carefully trimmed out of the matrix that I have no associated species to assist me. 



