350 PROCEEDINGS OF THE ACADEMY OF [May, 



into the early whorls, and they are mere tubercles. Their transforma- 

 tion into a shoulder keel is, however, essentially similar to the change 

 in F. carica. The tubercles become longer in a spiral direction, but 

 lower in height and soon merge into a shoulder keel. 



2, Swelling on the anterior siphon. — In senile individuals and species 

 the mantle, in the region of the anterior or branchial siphon, not infre- 

 quently bulges at a certain point. As the animal grows, this bulging of 

 the mantle produces a swollen ridge in the shell. The long diameter of 

 this swelling runs obliquely to the line of the shoulder angle, and in a 

 more anterior direction. Numerous dissections of Fulgur carica ha\'e 

 failed to show a cause for this mantle swelling. 



The two above marks of senility — that is, the passing of the spines 

 into a shoulder keel, and the swelling on the anterior siphon — are both 

 well shown in old individuals of the Fulgur carica of our New Jersey 

 coast. These two characters, together with a third (the tendency for 

 the anal siphon to encroach upward on the preceding whorl), are the 

 last ornamental features which occur on the oldest individuals. A w^ell- 

 marked sexual dimorphism occurs in this species. The full-grown 

 males are considerably smaller than the full-grown females. The old 

 males and old females show the senile characters above mentioned ; and 

 the difference in the size of the senile individuals of the different sexes 

 furnishes a I'eady method of determ'ning sex without reference to the 

 soft parts. These observations were made on a large series of Fulgur 

 carica}'^ 



3. Protrusion of the mantle in the region of the anal siphon, producing 

 a smoothing of the preceding whorl by -a shelly overgrowth. — This is beauti- 

 fully illustrated by several races of Volutilithes petrosus. In the later 

 whorls the mantle in the region of the anal siphon protrudes and tends 

 to wrap itself aroimd the preceding whorl. In the early stages of the 

 process we have little more than a smoothing of the preceding whorl. 

 The mantle soon passes up over the spines of the preceding whorl, and 

 the shelly deposit becomes thicker and thicker, completely obliterating 

 ornamentation, and making it in many cases extremely difficult to 

 count the whorls. Every stage of the process can be traced in indi- 

 vidual development; while several races make a series from forms in 

 which the mantle has been little protruded to forms in which it has 

 covered in the preceding whorl, obliterating ornamental features. It 

 does not necessarily follow that these races in question make a phylo- 

 genetic succession, but they unquestionably represent stages in the 



1" Proc. Acad. Nat. Sci. Phila., June, 1902. 



