FOSSIL CEPHALOPODS. 317 



Mr. Robert Etheridge, F.R.S., in his presidential 

 address to the Geographical Society of London, stated 

 that "the whole of the Secondary rocks, from the 

 base of the Lias to the highest Chalk, have been 

 subdivided and specialized by the Ammonitidce a 

 classification holding good for Europe, India, and 

 America, many species being the same both in the 

 eastern and western hemispheres." 



Perhaps the commonest species of Nautilus in the 

 Inferior Oolite is the elegantly shaped Nautilus hexa- 



Fig. 321. Crioceras. 



gonus. It is found in the " Cornbrash " of Northamp- 

 tonshire, Kellaways rock, and other subformations. 



I ought to mention that certain fossils called 

 Trigonellites are found in the Secondary strata, and 

 that they have always been regarded as the "oper- 

 cula," or " doors " of Ammonites. The late Charles 

 Moore, F.G.S., of Bath, was strongly against this 1 

 notion. 



In those subdivisions of the Oolite which are of 



