1905. 



NATURAL SCIENCES OP PHILADELPHIA. 



353 



spine is met with on a rounded whorl. Here, as above, the condition 

 is accompanied by other senile features. 



Recurrent or discontinuous ornamentation is also met with in the 

 sinistral Fulgurs of the Miocene, in not a few Stromhs, and in some indi- 

 viduals of Volutiliihes dalli. In the last mentioned, the breaks in a 

 particular style of ornamentation may occur early in life, but the shell 

 always shows senile characters in its last whorls. 



Senile Offshoots from Main Ancestral Stems. 



In no group of gastropods are senile offshoots from main lines of 

 descent so well marked as in the Fulgurs. The modern Fulgur carica 

 of our New Jersey coast is a simple, little accelerated type which, 

 however, shows well-defined senile characters in its last whorl. 



In the Yorktown Miocene of North Carolina occiu- certain formg 

 which were described by Conrad as Fulgur striatum. Some of these 

 small forms are undoubtedly the young of Fulgur maximum, as can 

 be seen in the early degeneration of the tubercles, but others whose 

 tubercles increase in size can hardly be distinguished from the young 

 of Fulgur carica. It is from these latter, or from very closely allied 

 forms, that the modern New Jersey Fulgur carica is descended. The 

 main line of the ancestry of Fulgur carica may be represented as 

 follows : 



This has been a slow and even evolution, marked by increase in size, 

 stronger and continuous spine development, and finally in the old indi- 

 viduals of Fulgur carica by the appearance of the senile characters 

 in the last whorl, which have already been referred to. 



In the Yorktown Miocene the Fulgur maximum branch Was evolved. 

 As can be seen by examining the young Fulgur maximum, it owes its 

 ancestry to the ancestral Fulgur carica. It differs from this form, 

 however, in the early degeneration of the shoulder angle tubercles — 

 a tendency which soon results in a rounded, lirate and relatively thin 

 whorl. This spineless condition continues for some time, but in the 

 later whorls secondary spines appear. This recurrent ornamentation 

 is accompanied by shell thickening, encroachment upward of the anal 



