AMMONITES— ZOOLOGICAL^ ETC. 



105 



the complication of the ornaments continues to increase 

 during the existence of the Ammonite. 



Number of lobes, — I have already stated, that the Am- 

 monites are always provided with at least the six primitive 

 lobes. Amongst those which are only provided with these, 

 are, A. subfimbriatus, Honnoratianus, quadrisulcatus, stria- 

 iisulcatuSj strangularis, and Juilleti of the Cretaceous rocks, 

 and A. fimbriatus of the Jurassic formation, the lobes and 

 saddles are at their greatest number, and only become more 

 complicated in their ornamental parts 3 but this is not 

 the case with those Ammonites, which ultimately acquire 

 a larger number of lobes. They have frequently, one or 

 two auxiliary lobes in the embryo state, as we find in 

 A, interruptuSf and the number at this period, is always 

 dependant on the number they ultimately attain. The 

 others appear successively at different periods of the growth, 

 till they arrive at their maximum number, which generally 

 takes place at the adult period, or the second period of 

 growth. 



In conclusion, age produces no changes in the modifi- 

 cations of the septa except 1st. in the complication of the 

 ornaments of the divisions, which exist in the embryo 

 period, and become more developed during the existence 

 of the Ammonite ; 2nd. in the number of the auxiliary 

 lobes, which takes place chiefly during the earlier period of 

 the animal existence : thus, by always comparing individuals 

 of the same size, as to the number, form and details of 

 the lobes, we shall acquire certain information as to the 

 identities, or differences which exist, and we shall be posi- 

 tively assured, whether the individuals are the same, or 

 distinct species. By always choosing an adult individual, 

 when examining the septa, we shall find the divisions 

 complete. The variations arising from age will en- 

 tirely disappear, and the internal characters of the 



