68 THE NAUTILUS. 



edge of the oyster is brought against the inner edge of the lip 

 with considerable pressure and then drawn inward and toward 

 the canal. A small piece is chipped from the edge of the oyster 

 and the process repeated until a gap is made large enough to 

 to admit the radula, which then tears out the flesh. This 

 method of getting at the animal explains not only the rough- 

 ened and chipped condition of the lip of the Busycon, but also 

 the chipped oyster and quahaug shells. Occasionally I have 

 found a live quahaug with its edge much chipped but still 

 intact, so the whelk does not always succeed. Usually, how- 

 ever, it encounters but little difficulty. 



DESCRIPTIONS OF NEW SPECIES FROM THE CRETACEOUS AND 



TERTIARY OF THE TESLA, PLEASANTON, SAN JOSE, AND 



MT. HAMILTON QUADRANGLES, CALIFORNIA. 



BY E. B. HALL AND A. W. AMBROSE. 



INTRODUCTION. 



During the paleontological work at Stanford University, for a 

 folio covering the Tesla, Pleasanton, San Jose and Mt. Hamilton 

 Quadrangles, several new forms were found. In order that the 

 names of these might be established, the writers decided to 

 publish the descriptions of the same. The writers' thanks are 

 due Dr. James Perrin Smith for his assistance to the writers in 

 this work. 



HORSETOWN MIDDLE CRETACEOUS. 



PECTEN CLARKENSIS n. s. Hall and Ambrose. 



Description. Shell small, two specimens found averaging 17 

 mm. in altitude, little higher than long, compressed, thin, sub- 

 circular, equivalve and equilateral ; ears equal, moderately 

 small, base regularly rounded, margins smooth. Surface 

 marked by 20 or 21 radiating nearly equal ribs, being two or 

 three times the width of interspaces that terminate abruptly a 

 little way from margin, also by obscure lines of growth. 



Dimensions. Alt., 16mm.; latitude, 16mm.; longitude, 

 18 mm. ; hinge line (restored and approximate) 9 mm. ; diam- 

 eter, 11 mm. 



