FOSSIL CEPHALOPODS. 



325 



generally, wherever the chalk marl is worked, many 

 of these forms o{ Ammonitidce will be found. A good 

 many true Ammonites range to the veiy highest 

 part of the Norfolk Chalk, which is, perhaps, the 

 highest horizon in England — such as Ammonites RJio^ 

 tomageusis^ etc. 



Fig. 330. — PJiTagvioceras vcntricosuin. 



The Belemnites belong to the Dibranchiate (or two- 

 gilled) division of Cephalopoda. The fossils known 

 by this name are the hard internal parts or " guards " 

 of an extinct family of cuttle-fishes. It will be seen, 

 in a perfect Belcmnitc, that the upper and thicker 



Y 



