66 CRETACEOUS GROUP 



Cardium. 



1. Casts of a smooth species are common in all the 

 strata : they vary in size from half an inch to an inch in 

 length. 



2.? Larger, ventricose casts, strongly ribbed. 



Cardita. 



C. decisa, (S. G. M.) PI. ix, fig. 3. 



Specific character. Subtriangular, ventricose, longitudinally 

 striated and transversely undulated ; posterior end truncated ; 

 margin straight. 



From the blue marl of St. Georges, Delaware. 



I am not positive that this cast is from a Cardita ; but 

 it most resembles this genus, and is unlike any other marl 

 fossil with which I am acquainted. 



Crassatella. 



C. vadosa, (S. G,M.) PI. xiii, fig. 12. 



Specific character. Ovato-triangular, slightly compressed; 

 with about thirty distinct, concentric striae. 



Length, one inch and a quarter ; breadth, one inch. 



From the older cretaceous strata at Prairie Bluff, Ala- 

 bama. Mr. T. A. Conrad. Casts of this genus are not 

 uncommon in New Jersey. It is probable that the black- 

 ish ones so common in the neighborhood of Long Branch, 

 belong to Crassatella. Mr. Vanuxem has spoken of them 

 as Mytili, in which I followed him $ but there can be no 

 doubt of this being a mistake. 



