104 



the shell may have been removed by decomposition; whilst the na- 

 cre, which has remained, in consequence of some peculiarity of struc- 

 ture or of composition, assumes the appearance of being the real 

 external shell. 



The nautilites of Sheppey particularly engaged the attention of the 

 late Mr. William Jones, who, speaking of those which are imbedded in 

 septaria, observes : " When this shell (Nautilus) is found lodged in the 

 waxen vein, a phenomenon is observable in some of the specimens, 

 which seems the most surprising and unaccountable of any that occurs 

 in this branch of philosophy. The stone is quartered irregularly into 

 tali or cubes, by seams of a coarse yellow spar, of the colour of beesr 

 wax, which intersect the stone in many directions : and what is won.- 

 derful to see, these seams of spar pursue their course through the sub- 

 stance of the nautilus, as if nothing had been interposed, though the 

 shell is nearly as impenetrable as a flint. The case is very difficult, if 

 we consider it as a penetration of the shell : but perhaps, when the shell 

 was detained within the stone, it was obliged to part and crack, by the 

 subsequent shrinking of the stone; so that when the spar filled the 

 seams of the stone, it filled up the crevices of the shell at the same time. 

 The insinuation of the spar through the siphunculus, and its forming a 

 column within the chambers of the shell, is another remarkable cir- 

 cumstance. Upon the whole> the nautilus, thus inclosed, and affected 

 by the waxen vein, is one of the most curious fossils in the world *." 



In the neighbourhood of Whitby, situated on the sea-coast, in the 

 North Riding of Yorkshire, a species of nautilites is found, which dif- 

 fers from the preceding in the back part of the shell, or of its turns 

 being flat instead of round : so that the sides go off almost at a right 

 angle from the back of the shell. 



Between Bath and Bristol, in the neighbourhood of Keynsham, there 

 is sometimes found another species, in which the back of the shell is 



* Physiological Disquisitions, &c. by William Jones, F.R. S. p. 392, 1781, 



