MOLLUSCA- 227 
testaceous matter ; in the latter, the matter seems to be ac- 
cumulated against the internal opening of some hole with 
which the shell has been pierced by some of its foes. _Lin- 
nzeus, from the consideration of this circumstance, endea- 
voured, by piercing the shell, to excite the animal to se- 
crete pearl ; but his attempts, though they procured him a 
place among the Swedish nobility and a pecuniary reward, 
were finally abandoned ; the process being found too tedi- 
ous and uncertain to be of any public utility. The largest 
pearl of which we have any notice, is one which came from 
Panama, and was presented to Philip II. king of Spain, in 
1579. It was of the size of a pigeon’s egg. Sir Robert 
Sibbald mentions his having seen pearls from the rivers of 
Scotland as large as a bean. 
Besides yielding us a variety of wholesome food, and valu- 
able ornaments, testaceous animals supply us with a beauti- 
ful dye. The Purpura of the ancients, according to the 
opinion of Rondeletius, confirmed by the observations of 
Cuvier, was chiefly extracted from the shell termed Murex 
brandaris. Since the introduction of the cochineal insect, 
the use of this dye has been superseded, so that we are now 
in a great measure ignorant of the process which the an- 
cients employed to extract it. In Britain there are several 
kinds of shell-fish, which furnish a dye of this sort, but these 
are seldom sought after. Cole, in 1685, published a method 
of obtaining it from the Purpura lapillus, to which Mon- 
tagu, in the supplement to Testacea Brittaniea, has added 
several important directions. When the shell is broken in 
a vice, there is seen on the back of the animal, under the 
skin, a slender longitudinal whitish vein, containing a yel- 
lowish liquor. When this juice is applied to linen, by means 
of a small brush, and exposed to the sun, it becomes green, 
