Cl. VI. MACTRA. FLAT-SIDED COCKLE. 197 



Mont. Test, Br. Sup. 37« 15. minutis* 



SIMA. 



* M. with a white, smoothish, triangular shell ; 

 back prominent ; single large tooth in one valve, 

 enters between two in the other. One of the 

 most minute of bivalves. 



