354 PROCEEDINGS OF THE ACADEMY OF [May, 



siphon on the preceding whorl, and the sweUing on the anterior siphon 

 — all senile features. This is the method by which most of the indi- 

 A'idiials recognized as Fulgur maximum have been evolved. Some- 

 times, however, recurrent ornamentation is only slightly marked, the 

 spines occurring at long intervals on the rounded whorls. 



The whole assemblage shows every indication of being a senile off- 

 shoot. Every large individual shows senile characters. The main 

 Fulgur maximum branch (including the forms described as F. maxi- 

 mum, F. tritonis, F. filosum) becomes extinct at the end of the Miocene. 



Shortly after the divergence of the Fulgur maximum branch from the 

 main Fulgur carica stem, a series of forms with rounded whorls diverged 

 from the maximum stock. Their young are much like the young 

 of Fulgur maximum, but the tubercles degenerate at a more early 

 period. This short tubercled stage Ls followed by thin, rounded, spine- 

 less whorls in the vast majority of individuals, resulting in the form 

 known as Fulgur rapum. A few senile individuals of Fulgur rapum 

 exhibit a thickening of the last whorl, and recurrent or discontinuous 

 ornamentation, in the shape of secondary spines. Fulgur rapum 

 becomes extinct with the end of the Pliocene. 



In Pliocene or Recent times a branch has been evolved from the 

 Fulgur carica main stem which has resulted in such forms as Fulgur 

 eliceans. These are senile and exhibit an acceleration of characters 

 accompanied by very high spines. These spines are not as numerous 

 as in Fulgur carica. They sometimes tend to pass into a shoulder keel, 

 though less often than in Fulgur carica. In other respects, however, 

 these forms show extreme senility — the swelling on the anterior siphon 

 is very large, the shell is very heavy and the anal siphon encroaches 

 upward. 



The phylogeny of Fulgur carica and allied forms may be represented 

 as follows: 



