274 



HISTORICAL PALAEONTOLOGY. 



forms of Ammonitidcs constitute one of the most conspicuous 

 features in the Ufe of the Chalk period. 



The Dibranchiate Cephalopods are represented partly by the 



Fig. 203. — Turrilites 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 EmericinnuTn, reduced 

 — Lower Greensand ; b, Baculites aticeps, reduced 

 — Chalk : c. Portion of the same, showing the folded 

 edges of the septa ; d, Crioceras cristatittn, reduced 

 — Gault; e, Scaphites ceqnalis, natural size — Chalk; 

 /, Hantites rotutidits, restored — Gault. 



beak-like jaws of unknowTi 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 



