282 



HISTORICAL PALAEONTOLOGY. 



ever complex, may be regarded as being simply produced by 

 the bending or folding of such a conical septate shell in differ- 

 ent ways. The Baculite, therefore, corresponds, in the series 



Fig, 203. Turrilites cate- 

 nate*. The lower figure rep- 

 resents the entire shell ; the 

 upper figure represents the 

 base of the shell seen from 

 below. Gault. 



Fig. 204. a, Ptychoceraa Emericicmum, , reduced 

 Lower Greensand ; &, Saculites anceps, reduced 

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

 edges of the septa ; a, Crioceras cristatum, reduced 

 Gault ; e, Scaphites cequalis, natural size Chalk ; 

 /, Hamites rotundus, restored. Gault. 



of the Ammonitida, to the Orthoceras in the series of the Nau- 

 tilidce. All the above-mentioned genera are characteristically, 

 or exclusively, Cretaceous, and they are accompanied by a 



