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 colourino; 
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. 
