274 HISTORICAL PALZONTOLOGY. 
forms of Ammonitide constitute one of the most conspicuous 
features in the life 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 Emericianum, reduced 
—Lower Greensand; 6, Baculites anceps, reduced 
—Chalk ; c, Portion of the same, showing the folded 
edges of the septa; da, Crioceras cristatum, reduced 
—Gault; e, Scaphites egualis, natural size—Chalk ; 
J, Hamites rotundus, 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 
