the gaper, in zoology; a genus belonging to the order of vermes testacea, the characters of which are these. It has a bivalve shell gaping at one end; the hinge, for the most part, furnished with a thick, strong, and broad tooth, not inserted into the opposite valve. Its animal is an Ascidia. The most remarkable species are:

1. The declivis, or sloping mya, has a brittle half-transparent shell, with a hinge slightly prominent near the open, and sloping downwards. It inhabits the rivers of Europe. It is frequent about the Hebrides; the fish eaten there by the gentry.

2. The mya pictorum has an oval brittle shell, with a single longitudinal tooth like a lamina in one shell, and two in the other; the breadth is a little above two inches, the length one. It inhabits rivers. The shells are used to put water-colours in, whence the name. Otters feed on this and the other fresh-water shells.

3. The margaritifera, or pearl mya, has a very thick, Fig. 3. &c., coarse, opaque shell; often much decorticated; oblong, bending inward on one side, or arcuated; black on the outside; usual breadth from five to six inches, length two and a quarter. It inhabits great rivers, especially those which water the mountainous parts of Great Britain.—This shell is noted for producing quantities of pearl. There have been regular fisheries for the sake of this precious article in several of our rivers. Sixteen have been found within one shell. They are the disease of the fish, analogous to the stone in the human body. On being squeezed, they will eject the pearl, and often cast it spontaneously in the sand of the stream. The river Conway was noted for them in the days of Camden. A notion also prevails, that Sir Richard Wynne of Gwydir, chamberlain to Catha-

Vol. XII. Part II. Mya queen to Charles II. presented her majesty with a pearl (taken in this river) which is to this day honoured with a place in the regal crown. They are called by the Welsh *craig dilw*, or "deluge shells," as if left there by the flood. The Irt in Cumberland was also productive of them. The famous circumnavigator, Sir John Hawkins, had a patent for fishing in that river. He had observed pearls plentiful in the Straits of Magellan, and flattered himself with being enriched by procuring them within his own island.

In the last century, several of great size were got in the rivers of the counties of Tyrone and Donegal in Ireland. One that weighed 36 carats was valued at £100, but being foul, lost much of its worth. Other single pearls were sold for £1.10s. and even for £10. The last was sold a second time to Lady Glenleavy, who put it into a necklace, and refused £800 for it from the duchess of Ormond. Suetonius reports, that Caesar was induced to undertake his British expedition for the sake of our pearls; and that they were so large that it was necessary to use the hand to try the weight of a single one. Mr Pennant supposes that Caesar only heard this by report; and that the crystalline balls called *mineral pearl*, were mistaken for them. We believe that Caesar was disappointed of his hope; yet we are told that he brought home a buckler made with British pearl, which he dedicated to, and hung up in, the temple of Venus Genetrix: a proper offering to the goddess of beauty, who sprung from the sea. It may not be improper to mention, that notwithstanding the classics honour our pearl with their notice, yet they report them to have been small and ill-coloured, an imputation that in general they are still liable to. Pliny says, that a red small kind was found about the Thracian Bosphorus, in a shell called *mya*; but does not give it any mark to ascertain the species.

Linnaeus made a remarkable discovery relating to the generation of pearls in this fish.—It is a fish that will bear removal remarkably well; and it is said, that in some places they form reservoirs for the purpose of keeping it, and taking out the pearl, which, in a certain period of time, will be again renewed. From observations on the growth of their shells, and the number of their annular laminae or scales, it is supposed the fish will attain a very great age; 50 or 60 years are imagined to be a moderate computation. The discovery turned on a method which Linnaeus found, of putting these shell-fish into a state of producing pearls at his pleasure; though the final effect did not take place for several years: He says, that in five or six years after the operation, the pearl would have acquired the size of a vetch. We are unacquainted with the means by which he accomplished this extraordinary operation; but it was probably published at the time, and considered as important, since it is certain that the author was rewarded with a munificent premium from the states of the kingdom on this account. We regret that we cannot speak more fully on this head; but may observe, that it is probable, from a paper published many years afterwards in the Berlin Acts, that the method consisted in injuring the shell externally, perhaps by a perforation; as it has been observed, that these concretions in shell-fish are found on the inside, exactly opposite to perforations and injuries made from without by serpents and other animals.