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HISTORICAL PAL/EOXTOLOGY. 



forms of Ammoniiida constitute one of the most conspicuous 

 features in the life of the Chalk period. 



The Dibranchiate Cephalopods are represented partly by the 



Fig. 203. Turrilitcs cate- 

 natus. The lower figure rep- 

 resents the entire shell ; the 

 upper figure represents the 

 base of the shell seen from 

 below. Gault. 



Fig. 204. a, Ptychoceras Emericlannm, reduced 

 Lower Greensand; b, Baculites anceps, reduced 

 Chalk ; c, Portion of the same, showing the folded 

 edges of the septa ; d, Crioceras cristatum, reduced 

 Gault ; e, Scaphites a-qnalis, natural size Chalk ; 

 /, Hamites rotnndus, restored Gault. 



beak like jaws of unknown species of Cuttle-fishes and partly 

 by the internal skeletons of Belemnites. Amongst the latter, 

 the genus Belemnites itself holds its place in the lower part of 



