218 ARCA. ARK-SHELL. Class VI. 



9. TENUIS. Mont. Test. Br. Sup. 56. t. 2Q. f. 1. 



* A. with a smooth subcordate shell, white with 

 an olivaceous epidermis ; beaks near one end 

 slightly inflected; greatest diameter a quarter 

 of an inch. 



Found on the shore near Dunbar. 



