62 CRETACEOUS GROUP 
Piacuna, Lam. 
P. scabra (S. G. M.) 
Specific character. With numerous beaded coste, radiating 
from the hinge to the margin; shell thin, suborbicular, com- 
pressed. 
From one inch to three inches in diameter. 
Found hitherto only in fragments in the blue marls. 
PLIcATULA, Lam. 
P. urticosa, (S.G. M.) PI. x, fig. 2. 
American Journal of Science, vol. Kkiv, pl. x, fig. Q, 
Specific character. Irregularly oval, flattened, thin, grega- 
reous; with fifteen or twenty squamous coste, some of which 
bifurcate near the margin. 
Length, an inch and a half; breadth, an inch. 
Found in the arenaceous marls of New Jersey and Ala- 
bama, by Mr. Conrad. 
Referred in the former edition to Ostrea. 
INOCERAMUS. 
1. I. Barabini, (S.G.M.) PI. xvii, fig. 3, and pl. 
xill, fig. 11. 
Specific character. Obliquely elliptical, not ventricose, 
with concentric, prominent, subacute ribs: beaks prominent, 
approximate. 
This species is extremely variable both in outline and 
size. Pl. xvii, fig. 3, represents an imperfect specimen 
of a large size ; and pl. xiii, fig. 11, shows another much 
smaller, but with a nearly entire margin. From the older 
cretaceous strata of Greene county, Alabama. 

