﻿Phylogeny 



.OF AN... 



Acquired Characteristic 



BY ALPHEUS HYATT. 



Extracted from Proceedings American Philosophical Society, 

 Vol. xxxii, No. 143. 



Preface. 



This memoir was first given as a short address before the American 

 Philosophical Society of Philadelphia, at the celebration of the one 

 hundred and fiftieth anniversary of the foundation of that illus- 

 trious body. A short preliminary abstract was subsequently pub- 

 lished in their Proceedings and in the American Naturalist for 

 October, 1893, with one diagrammatic plate. The statements 

 made in these two preliminary papers before all the facts were 

 brought together and correlated were true, in the main, but 

 necessarily defective and have been put into more correct shape in 

 the following pages. 



Introduction. 



The nature of the evidence afforded by fossil shells is even at the 

 present time very little understood. They have been so often spoken 



