186 POPULAR BRITISH CONCHOLOGY. 



to be distinguished from the tubercular swellings of 

 many fusiform shells. 



II. Lachesis minima. — A very minute mollusc, with a 

 fusiform shell, which, during the life of the animal, is of a 

 dark-brown colour, but after death becomes reddish. 



III. Purpura. — The genus to which this name is now 

 applied does not include the mollusc from which the Tyrian 

 purple of antiquity was procured. That historical honour 

 belongs pre-eminently to the Ilurex tmncuhs, and, in a se- 

 condary degree, to other species of Murex. Nevertheless 

 the PurjmriB, like their more splendid neighbours, do secrete 

 a fluid quite as capable of imparting the royal tint to any 

 fabrics dipped in it. Behind the head in 'Purpura lajnllusj 

 the only species our islands possess, is a receptacle contain- 

 ing a white fluid, which, on exposure to the air and light, 

 reaches a brilliant purple tint through several intervening 

 gradations of yellow, green, and blue. Tlie dye so obtained 

 is made permanent without difficulty; but, although it was 

 formerly used in Irish marmfacture, it lias long since ceased 

 to be so employed, — perhaps through not being procurable 

 in sufficient quantity to make it worth collecting. 



The shell is oval or fusiform, rather stout, with a thick 

 outer lip, and a well-defined canal ; the whorls of the spire 



