* 



AMMONITES BILLINGSI. 317 



branching of the lobes and saddles of its septa, that can- 

 not be due to different stages of development. In addi- 

 tion to this, I found along with it a much smaller specimen, 

 evidently the young of A. Barnstoni, which shows that 

 the young of that species did not vary in form materially 

 from the adult, and is quite different from the species now 

 under consideration. 



It has much the form of A. Halli, Meek and Hayden 

 (Proceed. Acad. Nat. Sci. Phil., vol. viii. p. 70), and 

 there are no differences in the structure of the dorsal 

 lobes of the two, that might not be due to different degrees 

 of development. Their superior lateral lobes and dorsal 

 saddles, however, present radical differences, such as we 

 never see in the same species, however widely they may 

 differ in size or age. 



I have named this species in honour of Mr. E. Billings, 

 the accomplished Palaeontologist of the Canadian Geolo- 

 gical Survey.] 



