THE MOEPHOLOCIY OF THE AMMONITE SEPTUM. [vol. Ixxiii. 



septum could not be expected to throw light upon the possible 

 complications which might arise in the future in a progressive series. 

 On the other hand, sections of a complicated septum such as that 

 of Lytoceras might reasonably be expected to show resemblances 

 to the sutures of any species of Baculites of Lytoceratan origin. 

 Replying to Dr. Da vies, he expressed the opinion that the presence 

 of coai'se ornamentation on the surface of an ammonite would not 

 seriously impair the usefulness of septal sections. The resemblance 

 of the inner pai't of the septum to the early septa was not really 

 an example of the phenomenon defined in the phrase ' localized 

 stages in development.' 



[April 6th. 1 91 8.1 



