OF THE UNITED STATES. 65 
before; beak prominent and incurved; shell thick, with nume- 
rous delicate, longitudinal striz. 
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.) PI. xiii, fig. 6. 
Specific character. An extremely ventricose cast, marked 
with numerous: longitudinal strie; 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.) PI. xv, fig. 13. 
Specific character. Obovate, with oblique very prominent 
ribs, about twelve in number. 
Among a great number of casts of Trigonie 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 
