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. 0. torosa, (S. G. M.) PI. x, fig. 1. 



Specific character. Elongated, with strong, squamous longi- 

 tudinal costse, intersected by transverse ridges. 



Length, five inches ; breadth, three inches. 



The squamous disposition of the costse, gives this shell 

 a coarsely reticulated aspect. I found at Mullica Hill, 

 New Jersey, a solitary individual, replaced by siliceous 

 matter. 



5. 0. sellxformis, (Conrad, Fossil Shells &c. PI. 

 xiii.) 



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, (S. 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. 



