6 PROCEEDINGS OP THE NATIONAL MUSEUM vol.7 



EXPLANATION OF PLATES 



[All figures natural size] 



Plate 1 



Ostrea center ensis Stephenson (p. 2) 



Figure 1. Exterior of the left valve of the type. Cat. No. 73657, U.S.N.M. 



2. Exterior of the right valve of the type, showing also overlapping 



margins of the left valve. 



3. Interior of a right valve from Cottonwood Creek, 2.7 miles north- 



northwest of Hutto, Williamson County. Cat. No. 73658, U.S.N.M. 



Plate 2 



Ostrea eenterensis Stephenson (p. 2) 



Figure 1. Exterior of a large left valve from Little Walnut Creek, 2% miles 

 southwest of Sprinkle, Travis County, showing its scar of attach- 

 ment to an elongated pelecypod shell. Cat. No. 73659, U.S.N.M. 



2. Interior of the same left valve. 



3. Front edge view of the type (Cat. No. 73657 U.S.N.M.), showing 



the thickness of the shell with the two valves tightly closed. 



Plate 3 



Exogyra tigrina Stephenson (p. 4) 



Figure 1. Exterior of the left valve of the type, showing the original color mark- 

 ings. Cat. No, 73660, U.S.N.M. 



2. The same, photographed after coating with ammonia chloride to 



cover up color markings, and bring out the true sculpture. 



3. Edge view of the same showing thickness and color markings. 



4. Interior of the same. 



5. Exterior of the right valve of the type, showing the overlapping 



margins of the left valve. 



6. Interior of the right valve of the tjipe. 



C. S. GOVERNMENT PRINTING 07FICB:1029 



