MOLLUSCS 91 



India — is of great importance as a religious emblem, 

 being the object of a special fishery. It is sold by the 

 tens of thousands in Bengal, where it is used in the manu- 

 facture of bracelets and anklets. One species of whelk 

 in the tropics (Fasciolaria) holds the record for being 

 the largest known Gastropod, specimens attaining a 

 length of 2 ft. 



The beautiful Rock Whelks QAurex) are very ornamental 

 and display numerous long and strong spines which must 

 deter the most voracious fish. The common Mediter- 

 ranean species may lay claim to fame as having provided 

 the famous " Tyrian purple " — the rich dye that was once 

 the sole prerogative of kings. This dye is common to all 

 the Rock Whelks, even to our native Dog Whelk (Nassa 

 reticulata), and is secreted by special glands. When first 

 extruded it is a pale yellow, but on exposure to sunlight 

 turns green and finally purple. In ancient times this 

 dyeing industry was practised throughout Italy and Greece, 

 and all along the south coast of France one may still meet 

 huge kitchen middens of empty Murex shells, testifying 

 to a fashion long since passed into oblivion. 



The big globular shells of the Barrel Whelks (Dolium) 

 are common in tropical seas where the animal is unique in 

 its method of attack. Its salivary glands secrete a fluid 

 containing over three per cent, free sulphuric, and fifty 

 per cent, free hydrochloric acid, with which it dissolves 

 the shells of the sea urchins upon which it feeds. 



The Coral Whelks (Coralliophila) are nearly allied to 

 our active predaceous whelk, but have acquired a strangely 

 sedentary habit. The animal fixes itself, mouth upwards, 

 into a block of coral and then continually extends the 



