PLATE XVII. 

 Exogyra costata Say (p. 50). 



Figure 1. Exterior view of right or upper valve from the Ripley formation (Exogyra costata zone); Johnsons Hill, 4 

 miles north of Lumpkin, Stewart County, Ga. (U. S. Geol. Survey coll. 6418c). Shows surface characters; 

 costae faintly developed. 

 2. Left valve from the Selrna chalk (near base of Exogyra costata zone); "Bald Knob" on Joseph Reynolds 

 place, 3 miles west of Corinth, Alcorn County, Miss. (U. S. Geol. Survey coll. 6459). Shows coarser, wider 

 costse than on typical specimens and a rather strong development of concentric growth projections, also a 

 very large scar of attachment. 



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