210 PROCEEDINGS OF THE ACADEMY OF [March, 



portion is lamellose and bears flat, triangular processes in the 

 interspaces. Toward the beaks the cuticle is worn off. Hinge- 

 line two-thirds the greatest length of the shell, straight, strongly 

 angular at both ends. Anterior margin evenly rounded; basal 

 margin well-arched, the posterior end noticeably arcuate, oblique, 

 meeting the basal margin in a blunt angle. Cardinal area very 

 narrow, sunken behind the beaks, with an elevated margin; 

 slightly wider and less sunken in front. Hinge teeth small and 

 vertical in the middle, well inclined and larger toward the two 

 ends; a distinct though narrow ledge below the posterior teeth. 

 Interior pure white, slightly grooved and delicately striate radially 

 in the cavity of the valves, becoming very deeply grooved toward 

 the margins, the summits of the intervening ridges concave. 



Length 45, alt. 36, diam. 29 mm. ; sometimes larger, length 

 55, alt. 46 mm. 



East coast of Hondo (Miss A. C. Hartshorn). Types No. 

 79,009, coll. A. N. S. P. 



This species, of which we have six specimens from two sources 

 (Nos. 79,009, 78,7.49, 70,970), is distinguished by its well- 

 rounded contours, unusually narrow cardinal area, the marked 

 disparity in size of the valves, and the large number of ribs. Tt is 

 somewhat allied to A. disparilis Reeve, 6 of which we have speci- 

 mens from Singapore, but that is less orbicular, with more of a 

 ridge or angle denning the posterior slope, and densely lamellose, 

 not bristly, in the intercostal spaces. 



In some specimens of A. nipponensis the cuticle is greenish in 

 places. 



*A. disparilis of Kobelt's monograph is clearly a species different from 

 that of Reeve. 



