63 



OBSERVATIONS. 



A very common species on almost all parts of our 

 coast. — Say. 



I found it abundantly near Mobile Point, on the 

 the shore of the Gulf of Mexico, and also in the 

 Newer Pliocene strata of Maryland. It resembles 

 M. subtruncatttp Montagu. 



MACTRA NUCLEUS. 



Tab. XIV, /^. 6. 



SPECIFIC CHARACTER. 



Shell small, triangular, thick, with an obsolete con- 

 centric angle ; umbones flattened ; apices very acute ; 

 lateral teeth robust ; within pale brown. 



SYNONYME. 



Mactra nucleus, nobisy Journ. Acad. JSfat. Sci. 

 vol. 6, p. 258, pi. 11, fig. 4. 



OBSERVATIONS, 



This small species is distinguished from the pre- 

 ceding by its solidity and its angular surface, and by 



