PLATE XV. 



Exogyra poxderosa Roemer (p. 46). 



Figure 1. — Left or lower valve from the Tombigbee sand member of the Eutaw formation (Exogyra ponderosa zone, 

 Mortoniceras subzone) ; Plymouth Bluff, Chattahoochee River, 4 to 5 miles northwest of Columbus, 

 Lowndes County, Miss. (U. S. Geol. Survey coll. 6918). Shows umbonal ridge well developed. 



2. — Right or upper valve of the preceding individual, showing surface characters. 



3. — Interior view of the specimen shown in figure 2, showing hinge, adductor scar, and other internal charac- 

 ters. 



Exogyra ponderosa var. erraticostata var. nov. (p. 49). 



Figure 4. — Left valve from the base of the Selma chalk (Exogyra ponderosa zone, above the Mortoniceras subzone); 

 1 mile west of Cotton Gin Port, Monroe County, Miss. (U. S. Geol. Survey coll. 6888). Shows typical 

 ornamentation of this variety. 



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