4 PROCEEDINGS OF THE NATIONAL. MUSEUM vol. 80:aet. 9 



lated by the external sculpture; the ventral margin a little less so. 

 The hinge teeth increase in size from the center, both anteriorly and 

 posteriorly, and promptly bend anteriorly in the anterior portion 

 and posteriorly in the posterior portion. There are 12 teeth in the 

 anterior and 18 in the posterior half ; they increase in strength from 

 the center outward. The muscle scars are very prominent, smooth, 

 and elevated. 



Type. — U.S.N.M. No. 74827, the specimen figured, comes from 

 Panama, and measures : Length, 24.2 mm. ; height, 12.2 mm. ; diam- 

 eter, 13.4 mm. 



Remarks. — This species may be the shell figured by Keeve on 

 Plate 14, figure 92, of his Conchologia Iconica in 1844. He says it 

 was collected by Cuming, who found it attached to stones at St. 

 Elena, West Colombia (Ecuador). The figure certainly resembles 

 our species, which is easily distinguished from the Mazatlanic shell 

 by its much coarser sculpture. 



In addition to the above, our collection contains other specimens 

 from Panama, the Galapagos Islands, and one valve from Manta, 

 Ecuador. 



*. S. GOVERNMENT PRINTINO OFFICR: 1981 



