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 Chico 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, K Gen. 



Shell thick, flattened snbglobose. 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 Oxystcle, Phil., and Photi?iula, H. and A. Adams. From 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. 



PL 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 nie. 



