CEPHALOPODA. 



217 



and lobed instead of being simply curved. The nuniei'ous beautiful 

 shells allied to the Ammonites cannot be even mentioned hei-e ; but 

 it is to be remembered that they are princij^ally cliaracteristic of the 



Fig. 156. — Ammonites bi/nm.^, from tlio I.ias. 



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

 occurring in the older period (Palteozoic epoch) 



