AMMONITES — ZOOLOGiCAL^ ETC, fS 



all these causes of error^ we should often feel embarrassedj 

 even in entering on this undertaking with the most scrupu- 

 lous attention, if we had only had at our disposal the exter- 

 nal characters. We should have seen each inquirer arbi- 

 trarily extend or restrict the limits of species ; and the most 

 beautiful, the largest and the most useful of all the genera of 

 fossil shells, would have lost its importance in its applica- 

 tion to Geology, remaining more an object of simple curio- 

 sity for Collectors, than a means of just reasoning for Pa- 

 leontologists. Happily, it is not thus. A character long 

 unknown, that of the foliations of the Septa, and the form 

 and number of the lobes and saddles, have presented them- 

 selves to determine these limits in an indisputable manner, 

 and to clear away all uncertainty. We owe the first appli- 

 cation of this feature to Leopold von Buch. This celebrated 

 Geologist knew how to appreciate, in his first Memoir* all 

 the importance that this character ought to hold in fixing 

 the limits of species amongst the Ammonites; and in many 

 subsequent publication sf, he added to it several interesting 

 facts. Nevertheless, no one has since ventured to undertake 

 the study of the lobes or Septa, and we can scarcely, beyond 

 the excellent works of Von Buch, find that any Ammonites 

 have been studied in this latter point of view, and these, 

 without much exactness. It is certainly necessary to pay 

 scrupulous attention to the undertaking, and the Zoologist 

 who wishes to study the Ammonites thoroughly, ought to 

 apply himself strenuously to the elucidation of these difficult 

 characters, to examine them in detail, in order that he may 

 not proceed to correct errors on false principles, at the risk 

 of perpetuating them indefinitely. I have followed this plan, 



* Annales des sciences naturelles, 1829, tome XVII, p. 267. 

 t Annales des sciences naturelles, 1829, tome XVIII, p. 417, tome 

 XXIX, p. 5. 



