36 LINN^AN GENERA. 



minates the mouth of the person who eats it ; and it is remarked, that 

 contrary to the nature of other lish, which give Ught when they tend 

 to putrescence, this is more luminous the fresher it is ; and when dried, 

 its hght -will revive on being moistened either with salt water or fresh ; 

 brandy however immediately extinguishes it."* 



It is to be regretted, that the experiments made by chemists on those 

 animals, which have a luminous appearance in the dark, have not 

 been sufficiently decisive, to enable us to state the true cause of it ; but 

 there is every reason to believe that it proceeds fi-om phosphorus, which 

 is abundant in all animal bodies. 



ORDER SECOND 



BIVALVE SHELLS. 

 Genus 4.— MY A. 



Animal an Ascidia ; shell bivalve, generally gaping at one 

 end ; hinge, in most of the species, with a broad, thick, 

 strong, patulous tooth, not inserted in the opposite valve. 



Mya arenarla The Sand My a. Plate V. fig. 4. 



Transversely ovate, rounded behind ; tooth very broad, 

 thick, obtuse, projecting, and erect; with a small lateral 

 tooth. 



The Myse are to be found both in the sea and in rivers. The marine 

 kinds generally live under sand or sludge, and the place where they 

 lie is betrayed by a small hole, out of which they occasionally protrude 

 their siphon, which is placed at the posterior or upper end. Those 

 which inhabit rivers, are generally found in the mud at its bottom. In 

 some places the animals are used for food ; but what makes them of 

 considerable importance is, the quantity of pearls which they some- 

 times produce. As illustrative of the value of pearls produced by the 

 Mya margaritifera, (Unio margaritifera, Lamarck,) it may be men- 

 tioned that according to Camden, Sir John Hawkins had a patent for 

 fishing that shell in the river Irt in Cumberland. This sheU is weU 

 known in Britain, by the name of the Pearl Muscle. We are informed 

 in the Philosophical Transactions, that several pearls of great size 

 have been pro(*ured from the rivers in the counties of Tyrone and 

 Donegal in Ireland. One of them weighed 36 carats, and wotild have 

 been worth £40, but owing to its being impure, it lost much of its value. 

 Other pearls from the same places have sold from £4 10s., to £10 each. 



* Priestley's Optics, page 567. 



