M U R EX. 107 



apart as a distant branch of the family: for generic 

 characters^ when they lose their validity as such, 

 ought not at once to degenerate into mere specific 

 ones, but should, in subordination, collect the spe- 

 cies into natural divisions. 



As is frequently the case, the genus owes its de- 

 signation to a certain number of its shells which 

 are rough and rock-like. The PuRPURiE of the an- 

 cients form the second section. From these shells, 

 or rather from their inhabitants, was expressed the 

 famous Tpian dye, the costly purple which con- 

 stituted an attribute of imperial dignity. A single 

 vein situated near the head of the fish contains this 

 colouring liquor which was formerly considered so 

 precious, but has of late years yielded its claims on 

 public estimation to other purple dyes equally 

 beautiful and more easily attainable. 



The quality is not confined to this one family of 

 Testacea, but has been discovered in certain spe- 

 cies of Buccinum, and may very probably belong 

 to some Limaces which inhabit other genera. 



