River Pearls ; British and Foreign. 237
are known locally as Cragen las. The
Pearl-bearers are confined to the bar of the river, no Pearls being
found either in those mussels that are collected higher up or in those
found on the sea shore. Each Pearl usually presents in its centre a
dark-coloured hard granular nucleus ; and on careful microscopic
examination of the mussels from the bar of the Conway, Mr. Garner came
to the conclusion that the Pearls had usually been concreted around a
small parasitical Distomust.
Fresh-water
Pearls have been often found in mussels from the mountain-streams of
Cumberland, especially in the Irt and the Esk. In Camden's Britannia we read that "At the mouth of the little brook Irt, on
the sea coast, are bred a sort of shell-fish or mussel, which gaping
there, and sucking In its dewy streams, conceive and bring forth
Pearls, or (as the Poets call them) Shell-berries. The inhabitants
gather them up at low water, and sell them to the jewellers at London for a trifle, who make a considerable gain of them ......
Those
that are not bright and shining, commonly called Sand-Pearl (and such
are those found in these parts usually) are as useful in physick as the
finest, tho' not so beautiful. Dr. Lister says he has' found sixteen of them in one mussel, and asserts them to be "Senescentiunt Mnscukrum Vitia"—
