108 



THE GEOLOGIST, 



Being struck with this anomalyj I was desirous of ascertain- 

 ing, whether it took place from an early age ; and I found 

 (more curious still), that in the embryo period, the above 

 named species have the septa symmetrical, like other Ammo- 

 nites; that the dorsal lobe does not diverge on one side 

 until the shell commences to form the tubercules on the 

 back ; this is an uncommon example of a true metamor- 

 phosis,, in the position and form of the septa. Whilst I 

 look upon this irregularity as exceedingly curious, I by 

 no means consider that it is of any great value in the 

 classification of groups ; all the other characters being 

 similar in form to those of the allied species. It is but 

 anomaly. 



Another series of irregular septa, equally interesting, but 

 which cannot serve as the base for any group, is that which 

 we remark in A, Vibrayeanus and Morensis. In the first 

 instance, the lobes and saddles are entirely without any 

 division, or ramification; they are all rounded and entire, 

 but not angular, as in the Goniatites. In the second 

 instance, the divisions of the septa are less uncommon; 

 we can recognise distinct lobes, and saddles in the midst 

 of numerous confused foliations. 



Regular Septa. — The regular Septa may, by their forms, 

 and ramifications, be divided and subdivided to infinity, as 

 they undergo a large number of modifications. I have 

 already mentioned the number of the lobes, and their 

 connection with the external form; we will now examine 

 whether the other modifications are a{Fected by the same 

 cause. The Septa are composed of lobes and saddles, and 

 the lobes are divided into equal or unequal parts. 



Lobes divided into equal parts^, — I give this name to 



* Von Buch does not appear to have been aware of this mode of 

 division ; at least I find no trace of it in his works. 



