576 



PROCEEDINGS OF THE ACADEMY OF 



[Oct., 



F. canaliculatum 

 (Recent) 



F. canaliculatum 

 (Pleistocene) 



F. incile 



(Burwell Bay, 



James R. Miocene) 



Hypothetical 



F. canaliculatum ancestor 



perhaps identical with F. rugosum 



F. coronal um 

 (St. Mary's Miocene) 



\ 



F. rugosum 

 (St. Mary's Miocene) 



Hypothetical 

 F . coronatum ancestor 



Geological Range and Classificatory Value of Shell 

 Structures and Ontogenetic Stages. 



Studies in evolution may be undertaken with the object of deter- 

 mining either the phylogeny of biologic groups, such as families, 

 genera, species, or the phylogeny of organic structures. Though 

 these two lines of research can never be regarded as entirely separate, , 

 they nevertheless constitute rather widely different aspects of the 

 problem. Therefore, the results obtained in these present studies 

 will be summarized with the view of emphasizing the phylogeny of 

 structures. 



The Sutiiral Canal: 

 (a) Oligocene to Recent. 



{b) An ascendant character, becoming stronger and accelerating 

 with the progress of time. 



