Try these sites for information on Tyrian Purple and the molluscs that
produce it:

http://www.middlebury.edu/~harris/Classics/purple.html
http://www.chriscooksey.demon.co.uk/tyrian/
http://www.sanders-studios.com/tutorial/historyanddefinitions/pigmentspast.h
tml
http://www.virtual.co.il/orgs/orgs/tekhelet/brochure.htm

        Paul M.