part 1] ox THE MORPHOLOar OF THE .OrMOXITE SEPTUM. 57 



Figs. 4-6. Hoplites splendens. Diameter =34 mm. 



Fig. 4. Septum showing displaced siphuncle, ami distortion associated there- 

 vnth.. 



5 a. Suture of the same at 12 mm. 



5 h. Do. do. at 32 mm. 



6. Do. of another specimen. 



7. Hoplites raidinianiis. Folkestone. Suture. 



8. Hoplites auritus. Cambridge. View of venter showing displacement 



of the siphuncle, first to one side and then to the other. 



9. Psiloceras planorhis. Robin Hood's Bay. Shomng position of dis- 



placed siphuncle. 

 Figs. 10-15. Asymmetrical sutures of various ammonites. 

 Fig. 10. Cosmoceras jason. Buckinghamshire. 



11. ^ Normannites' hrailcenridgii. Mesvil. 



12. Aspidoceras perarmatiim. Faringdon. 



13. TJptonia jamesonl. 



14. Keplerites calloviensis. Ashton Keynes. 

 1.5. Dactijlioceras commvne. Whitby. 



IL= Internal lobe. ES = External saddle. L^ = Principal or first lateral lobe. 

 L'- = Auxiliary' lobe. S^ = First lateral saddle. M = Median plane. Sip. = 

 Siphuncle. 



Discussion. 



Dr. F. A. Batheji thanked Prof. Swinnerton for his well- 

 illustrated and lucid exposition. It had heen said that in science 

 the invention of a new method was worth more than the discovery 

 of a hundred facts. The instrument devised hy the Authors might 

 be applied to the reproduction of other complicated surfaces. The 

 ammonites illustrated had all been proo;ressive types, and apj^a- 

 rently the method was unsuitable when retrogression had set in. 

 In progressive types the study of a late-formed septum enabled one 

 to work backwards, but not forwards, to the unknown. Might it 

 not, however, he possible to forecast the lines of retrogression "r' In 

 any case, the method would facilitate the determination of affinities 

 and the plotting-out of definite series on which more secure in- 

 ferences could be based. 



Dr. A. M. Dayies said that the suggestion that septal sections 

 might be used as a means of studying the development of the 

 septum had been made to him in conversation by Mr. S. S. Buck- 

 man some years ago. He congratulated the Authors on their 

 success in demonstrating the truth of this suggestion. He enquired 

 as to how far coarse ornamentation would interfere with the aj)plica- 

 tion of the metliod, and Avhether it was really trustworthy in the 

 case of septa which had undergone catagenetic simplification. 



Prof. H. H. 8wl^^^'£KT0X thanked those present for the kind 

 reception given to the paper. Replying to Dr. Bathei*. he stated 

 that ' septal sections ' supplied a standard of the most direct line 

 of development leading up to the condition found in the particular 

 septum from wliich they had been made ; for that reason they would 

 not record any deviations from that line occurring during evolu- 

 tion or development. The study of the septal sections of a simple 



Q. J. G. S. No. 289. f 



