NO. 2297. BRACHIOPOD GENUS PLATYSTROPHIA—McEWAN. 401 



time and marks the acme of specialization wliich was reached by the 

 genus. 



The Ponderosa subgroup which is conspicuous in Maysville and 

 Lower Richmond time represents members of the genus which ex 

 pended their energy in acquiring large size and then became prema- 

 turely old while the race as a whole was progressive. 



The writer was unable to determine the relative abundance and 

 stratigraphic succession of European members of the genus. 



Davidson's figures, 12, 13, and 25 ^ are distinctly of the triplicate 

 type, and seem to be related to PlatystropJiia colheinsis Foerste. 

 Figure 14^ evidently marks a retrograde form of this species as is 

 indicated by the one plication in the sinus. 



» British Fossil Brachiopoda, vol. 1, pi. 38. 

 115690— 19— Proc.N.M.vol.56 26 



