1914.] NATURAL SCIENCES OF PHILADELPHIA. 577 



(c) Appearing in primitive forms of the Miocene after the begin- 

 ning of the fifth whorl {F. coronatum). 



(d) Appearing in a very specialized Pliocene form as early as the 

 middle of the third whorl (F. pyrum Caloosahatchie Race). 



(e) Though showing acceleration, its most notable changes are 

 due to exaggeration of its depth or of its width. 



(/) Its changes (variations or mutations) serve in part as a basis 

 for the species of systematists. Its persistence is of generic or 

 group value and serves to differentiate the canaliculate from the 

 non-canaliculate Fulgurs. 



The Noded Stage: 



(a) Oligocene to Recent in this group. 



(6) A declining character for this group, becoming weaker with 

 the progress of time. Accelerating more by compression than by 

 the dropping out of nodes. 



(c) Appearing in all forms at about the beginning of whorl two. 

 Closing the ontogeny of primitive forms of the Miocene (F. corona- 

 turn). 



(d) Disappearing in very specialized forms before the completion 

 of the fourth whorl {F. pyrum). 



(e) Though its termination may show widely different degrees of 

 acceleration, its most notable changes are due to its degeneration. 



(/) Its changes through acceleration and degeneration serve in 

 part as a basis for the species of systematists. Its persistence is of 

 no higher classificatory value, for it is a primitive feature widely 

 distributed among very diverse groups of marine gastropods. 



The Keeled Stage: 



(a) Miocene to Recent in this group. 



(b) An ascendant character in the fairly primitive species (F. 

 rugosum, F. canaliculatum) . A dechning character in the most 

 specialized {F. pyrum, F. incUe). 



(c) Appearing in more primitive forms toward the end of the 

 seventh whorl, in the most specialized toward the end of the fourth 

 whorl. 



(d) Terminating the ontogeny in fairly primitive forms (F. rugo- 

 sum, F. canaliculatum). Ending early in the sixth whorl of the most 

 speciahzed {F. pijrum Caloosahatchie Pliocene). 



(e) Changes due to compression, acceleration, degeneration, and 

 exaggeration are all well marked. 



(j) Its changes through compression, acceleration, degeneration, 



