MUREX. 95 



ought not at once to degenerate into mere specific 

 ones, but should, in subordination, collect the 

 species into natural divisions. 



The genus owes its designation to a certain 

 number of its shells, which are rough and rock- 

 like. The Purpura of the ancients form the 

 second section. From these shells, or rather from 

 their inhabitants, was expressed the famous Tyrian 

 dye, the costly purple which constituted an attri- 

 bute 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. 



