52 CRETACEOUS GROUP 
but it is very inconstant, and sometimes absent. Refer- 
red in the former edition to O. cristagalli. 
Chiefly found at St. George’s, Delaware, and since in 
South Carolina and Alabama, where it is one of the most 
characteristic fossils of the newer cretaceous strata. 
4. QO. torosa, (S.G.M.)_ PI. x, fig. 1. 
Specific character. Klongated, with strong, squamous longi- 
tudinal costz, intersected by transverse ridges. 
Length, five inches; breadth, three inches, 
The squamous disposition of the cost, gives this shell 
a coarsely reticulated aspect. I found at Mullica Hill, 
New Jersey, a solitary individual, replaced by siliceous 
matter. 
5. O. selleformis, (Conrad, Fossil Shells &c. PI. 
Xili. ) 
Mr. Conrad has ascertained that the O. radians is the 
superior valve of the present species, which occurs not 
only in the Eocene at Claiborne, Alabama, but also in the 
newer cretaceous strata in South Carolina. 
6. O. cretacea, (5S. G. M.) PI. xix. fig. 3. 
Specific character. Shell obovate, convex; obscurely rayed ; 
superior valve slightly convex; cardinal fosset broad; beak 
scarcely prominent. 
Common in the older cretaceous strata of Greene 
county, Alabama. ‘This species is very abundant in the 
bluff at Erie, where it constitutes a distinct stratum. It 
is also common in the calcareous strata of South Caro- 
lina. 
s- 
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