116 



THE MUREX. 



from their outer surface. In the murex these pro- 

 cesses are very numerous. 



Remarkable changes also occur in the interior of 

 the shell at different stages of its growth. On the 

 inner surface of the mitra, the volute, and other shells 

 of a similar kind, a layer of a hard, semi-transparent, 

 calcareous material, having a vitreous appearance, is 

 deposited. The thickness of the layer which thus lines 



