Ol. VI. MACTRA. FLJT-SIDED COCKLE. W7 



Mont. Test. Br. Sup. 37- 15. MiwuTis- 



* 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. 



