1914.] 



NATURAL SCIENCES OF PHILADELPHIA. 



578 



a course will be more fully discussed later and at present it is suf- 

 ficient to say that the morphologic sequence displayed l)y F. corona- 

 turn, F. rugosum, F. canaliculatum, and the two assemblages of 

 F. pynim is believed to be best interpreted in terms of the phylogeny 

 as follows: 



F. canaliculatum 

 (Recent) 



F. pyruin 

 (Recent) 



F. canaliculatum 

 (Pleistocene) 



F. pijrum 

 (Caloosahatchie Pliocene) 



Hypothetical 

 F. pyrum ancestor 



Hypothetical 



F. canaliculatum ancestor 



perhaps identical with F. rugosum 



F. coronatum 



(St. Mary's F. rugosum 



Miocene) (St. Mary's Miocene) 



Hypothetical 



F. coronatum 



ancestor 



F. rugosum has been reported from the Calvert and Choptank 

 formations. ^^ Both are older than the St. Mary's. As far as the 



11 Md. Geol. Surv. Miocene, p. 182. 



