88 UNIVALVES. 



colour, sometimes banded with brown or yellow. 

 Length rarely exceeds two inches, breadth one. 



The animal that inhabits this shell has two 

 slender tentacula bearing eyes about half way 

 up on the outside, the ends of the tentacula as 

 far as the eyes are retractile * like those of snails. 

 Its mantle forms a tube through which it 

 breathes ; it has a foot with a horny operculum. 

 Near to its head, and lying in a little furrow, is 

 a white vein which yields a beautiful purple tint, 

 supposed to be that so long celebrated as the Ty- 

 rian dye. In order to obtain this colour, the vein 

 which contains a tenacious yellow matter like 

 cream, is laid open with a needle. As soon as 

 this fluid is put on any substance, as silk, linen, 

 &c., and exposed to the air, the yellow assumes 

 at first, a brighter hue, but speedily turns to pale 

 green, then gradually becomes darker, until it has 

 obtained a blue cast, and from that it changes 

 to a purplish red, more or less deep according to 

 the quantity used. The succession of the tints is 

 accelerated by exposure to the rays of the sun. 

 The stain given by this animal fluid seems to be 

 indelible, bidding defiance to every chemical pro- 

 cess to obliterate it, and it might therefore be 

 most advantageously used as a kind of marking ink. 

 The Buccinum Lapillus is one of the most 

 common shells upon our coasts, adhering to 

 rocks quite up to high water mark. 



* Retractile, capable of being draw back, from the Latin 

 re back, and tract its drawn. 



