52 PROCEEDINGS OF THE ACADEMY OF [March, 



PHYLOGENY OF THE EACES OF VOLUTILITHES PETROSTJS. 



by burnett smith, ph.d. 

 Introduction. 



In a recent article * the author has described some of the shell char- 

 acters which, occurring in the later stages of Gastropod ontogeny and 

 phylogeny, mark the gerontic or senile condition of the individual or 

 of the race. It was seen that these senile features may at times be as 

 useful to the student of phylogeny as those of the earlier stages, which 

 latter have always received the more attention. In the paper referred 

 to, the attempt was made to show that the modern Fulgur carica of 

 our New Jersey coast is the descendant of a main F. carica stock, 

 which originated in Miocene time ; and that such forms as F. maxivium 

 and its allies, which had heretofore been regarded as ancestral by 

 Grabau ^ and others, are in reality not so at all, but senile offshoots 

 which at an early period in the history of the stock diverged from the 

 main line of descent. The paucity of individuals representing the 

 forms considered ancestral, and the extreme abundance of the speci 

 mens of senile forms, was a source of some embarrassment to the 

 author. It is therefore with considerable satisfaction that I am now 

 able, though in another genus {Volutilithes), to present a series in 

 which the forms comprising the main ancestral stock are nearly as 

 plentiful as those which represent the senile offshoots. 



The history of certain of the species of Volutilithes can be well traced 

 in the Eocene of our Gulf States, but nowhere better than in Alabama, 

 where the fine sections along the Alabama and Tombigbee rivers have 

 furnished abundant material for the study of the geological and geo- 

 graphical distribution of these forms. The races and species studied 

 range from the Matthew's Landing horizon in Alabama to the Jackson 

 horizon in Mississippi, and therefore represent a fair proportion of the 

 phylogenetic units through nearly the whole of the Eocene. They are 

 likewise restricted to a small geographical area, and the geological 

 sections in which they appear are unusually good. 

 . t 



* Senility among Gastropods, Proc. Acad. Nat. Sci. Phila., May, 1905. 

 2 Studies of Gastropoda, II — Fulgur and Sycotypus, Am. Nat., Vol. 37. 



