CEPHALOPODA. 



217 



and lobed instead of being simply curved. The numerous beautiful 

 shells allied to the Ammonites carmot be even mentioned here ; but 

 it is to be remembered that they are principally chara;Cteristic of the 



Fig. 156. — Ammonites Hfrons, from the Lias. 



Secondary period in geology, and that they are hardly known as 

 occurring in the older period (Palseozoic epoch) 



