PLATE XL 



In 16S4, Mr. Cole, of Bristol, described the process of extractino- 

 the purple of this shell, in the Philosophical Transactions. Llis ac- 

 count is as follows : 



" The Shells being harder than most of other kinds, are to be 

 broken with a smart stroke with a hammer, on a plate of iron, or firm 

 piece of timber (with their mouths downwards) so as not to crush the 

 body of the fish within; the broken pieces being picked ofF, there 

 will appear a white vein, lying transversely in a little furrow, or cleft, 

 next to the head of the fish, which must be digged out with the stiff 

 point of a horse-hair pencil, being made short and tapering. The 

 letters, figures, or what else shall be made on the linnen (and perhaps 

 silk too) will presently appear of a pleasant light green colour, and if 

 placed in the sun, will change into the following colours, i. e. if in 

 winter, about noon; if in summer, an hour or two after sun-rising, 

 and so much before setting; for, in the heat of the day in summer, 

 the colours will come on so fast, that the succession of each colour 

 will be scarcely distinguished. Next to the first light green, it will 

 appear of a deep green, and in a few minutes change into a sea- 

 green ; after which, in a few minutes more, it will alter into a 

 watchet-blue ; from that, in a little time more, it will be of a pur- 

 plish-red ; after which, lying an hour or two, (supposing the sun 

 still shining) it will be of a very deep purple-red, beyond which the 

 sun can do no more. 



" But then the last and most beautiful colour, after washing in 

 scalding water and soap, will (the matter being again put into the sun 

 or wind to dry) be of a fair bright crimson, or near to the prince's 

 colour, which, afterwards, notwithstanding there is no use of any 

 stiptick to bind the colour, will continue the same, if well ordered, 



