TO GEOLOGY. 45 



true Mactrffi. From the description and figures, I should 

 not hesitate to abstract them from that genus. M. De- 

 shayes gives fourteen species in his Tertiary Tables, six 

 are from the Miocene of Bourdeaux and Dax. In this coun- 

 try, Mr Say seems first to have observed it in the Tertiary 

 of Maryland.* More recently Mr Conrad has discovered 

 in the same formation two new species, M. ponderosa, at 

 St Mary's river, Maryland, and J\f. delumbis, at St James's 

 river, near Smithfield, Virginia. 



FAMILY CORBULEA. 



GENUS CORBULA. Brugiere. 



C. Jllabamiensis. Plate 1. Fig. 12. 



Description. Shell inflated, triangular-ovate, angular 

 behind, transversely and finely striate, inequilateral, very 

 inequivalve, anterior part the larger ; beaks incurved and 

 rather pointed ; tooth of the right valve large, pointed and 

 fitting under the beak of the left valve ; posterior basal 

 margin straight or slightly emarginated ; the two great 

 cicatrices distinctly impressed ; cavity of the valves deep. 



Diam. 7-20ths, Length .4, Breadth .7, of an inch. 



Observations. This is the largest species I have seen 

 from our formations. It has a strong resemblance to C. 



* Journal of the Academy of Natural Sciences of Philadelphia, vol. 4 3 

 p. 152. 



