372 PROCEEDINGS OF THE ACADEMY OF [July, 



It is difficult therefore to believe that spine production in Fulgur is 

 the result of reproductive activity when we regard these two Atlantic 

 Coast species, with equally well developed reproductive organs and 

 with presumably similar habits of oviposition, the one spineless and 

 the other spined. By an examination of the penis in the two species we 

 can select no character in one which should produce a spine, or in the 

 other case state why the protrusion of the penis should not produce 

 a spine. 



Considering now the shoulder keel, which seems to be the evolu- 

 tional successor of the row of spines, we know by actual observation 

 that the non-development of the penis in F. canaliculatum does not 

 necessarily affect the keel, while, on the other hand, an injured keel- 

 less individual may possess the organ in its normal condition. 



From these facts we can be reasonably confident that the shoulder 

 keel has no connection with reproductive activity. When it comes to 

 the spines, however, we can but say that there are no characters in 

 the penis of F. canaliculatum which we can definitely correlate with 

 the spineless condition of the shell, and in F. carica we can assign to 

 the different form of the organ no cause for the development of spines. 



