PLATE XVI. 



ExOGYRA POXDEROSA var. ERRATICOSTATA V&T. 110V. (p. 49). 



Figure 1 . — Left or lower valve from the base of the Selma chalk (Exogyra ponderosa zone, above the Mortoniceras sub- 

 zone): 1 mile west of Cotton Gin Port, Monroe County, Miss. (J. S. Geol. Survey coll. 6888). Shows a 

 rather weak development of the irregular costae, with fine costse well developed on the beak; the irregu- 

 lar costse are well developed on the anterior portion of shell (which does not show in plate). 

 2. — Exterior view of right valve of the preceding individual. 



Exogyra costata Say (p. 50;. 



Figure 3. — Left valve from the Ripley formation ostala /one.; Johnsons Hill. -1 miles north of Lumpkin, 



Stewart County, Ga. (TJ. S Geol Survey coll. 6418e). Shows the regular cost* typically developed. 

 ■1. — Another view of the preceding specimen. 



<:-l 



