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OK THE 



AMERICAN PHILOSOPHICAL mJCIETY 



HELD AT PHILADELPHIA 



FOR PROMOTING USEFUL KNOWLEDGE 



VOLUME XXI— NEW SERIES 



PART I 



Artulk l — TliK Morphology of the Skull of the Pelycosaurian Genm Dimetrodon. By E. C. Case 



THK AMERICAN PHILOSOPHICAL SOCIETY 

 104 South Fibth Strekt 



