OF THE UNITED STATES. 65 



before ; beak prominent and incurved ; shell thick, with nume- 

 rous delicate, longitudinal striae. 



Length, one inch and three-fourths ; breadth, one inch and 

 a quarter. 



Cordiform casts of this species are common throughout 

 the arenaceous deposits ; but I am indebted to my friend 

 Dr. Wm. Riley for the perfect shell from which the an- 

 nexed figure was drawn. 



2. C. antrosa, (S. G. M.) PL xiii, fig. 6. 



Specific character. An extremely ventricose cast, marked 

 with numerous longitudinal striae ; beaks prominent and in- 

 curved. 



Although I have only seen casts of this species, it is so 

 characteristic of the ferruginous sand, that I have ven- 

 tured to name and figure it. 



Nucula. 



I have seen a few small casts in a ferruginous clay, from 

 the vicinity of Bordentown, N. J. 



Trigonia. 



T. thoracica, (S. G. M.) PL xv, fig. 13. 



Specific character. Obovate, with oblique very prominent 

 ribs, about twelve in number. 



Among a great number of casts of Trigonise from New 

 Jersey and Alabama, I have but two with the shell re- 

 maining, one of which is seen on the annexed plate. Mr. 

 Conrad obtained it at Prairie Bluff, Alabama. 



This species is variable in outline, but is readily iden- 

 tified by its other characters. 



I 



