103 IXTEODUCTION TO COXCHOLOGY. 



The Cass ides are not very numerous. They chiefly in- 

 habit the Mauritius, Ceylon, the Philippines, and West 

 Indies ; two species are found in the Mediterranean, but 

 none on our own coast. 



Greek words signifying Murex and Turpiira were used 

 indiscriminately by ancient Greek writers, in reference to all 

 mollusks yielding a pui'ple dye; these became, in conse- 

 quence, objects of especial interest, on account of the 

 limited soui'ces for obtaining colour. 



The purple juice of the mollusk afi'ords, however, no 

 assistance to the lover of systems : it abounds alike in 

 animals of very dissimilar character, — in the Scalaria and 

 lanthina, equally with the Murex and Purpura ; — hence the 

 latter term was adopted by Lamarck, to distinguish the 

 genus under consideration, regardless of any property of 

 secreting a purple juice. 



Purpura differ exceedingly in their details of sculpture, 

 but are somewhat constant in colour. The well-known 

 P. lapilhis, of Europe, varies in both respects to such an 

 almost inconceivable degree, that no one, who has not 

 thoroughly examined numerous specimens, can correctly 

 estimate its protean character. 



Yariety is an attribute of creation, and nowhere is it 



