PLATE XIX. 

 Exogyra costata Say (p. 50). 



Figure 1. Left valve from the Peedee sand; Robinsons Landing, Cape Fear River, 50 miles above Wilmington in 

 Bladen County, N . C. (IT. S. Geol. Survey coll. 3356). Shows extreme development of concentric lamellae. 



2. Interior view of same specimen showing hinge, adductor scar, and other internal characters. 



3. Left valve from tongue of Selma chalk at top of Cretaceous (Exogyra costata zone, Liopistha protexta sub- 



zone); Old Canton Landing, Alabama River, Wilcox County, Ala. (U. S. Geol. Survey coll. 6439). Shows 

 narrow cost* characteristic of specimens from this subzone. 



4. Left valve from the Ripley formation (Exogyra costata zone, approximately the Liopistha protexta subzone); 



Owl Creek, 3 miles northeast of Ripley, Tippah County, .Miss. (U. S. Geol. Survey coll. 6464). This 

 specimen also illustrates the narrow costa; characteristic of specimens from the Liopistha protexta subzone. 



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