PATAGONIAN EXPEDITIONS I PAL/EONTOLOGY. 



EXPLANATION OF PLATE XX. 



PAGE 



Fig. i. OSTREA PATAGONICA d'Orb. . . ... . . . . no 



From beds, unconformably overlying Patagonian beds (? Tehuelche 

 formation); Darwin Station, San Julian. 



\a. Lower valve of an elongated individual. 



\b. Lower valve of a more elongate individual, showing distinct 



folds. 



\c. Upper valve of another elongate individual. 

 id. Upper valve of a very broad individual, showing a muscular 

 scar of the character of that of O. pyrotheriorum v. Ih. 



All the figures are natural size. 



(VOL. iv) 



