3G LINN^AN GENERA. 



I 



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

 contrary to the nature of other tish, which give light when they tend 

 to putrescence, tliis is more himinovis the fresher it is ; and when dried, 

 its light vfUl revive on being moistened either with salt water or fi-esh ; 

 brandy however immediately extinguishes it."* 



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

 animals, which have a Imninous 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 from phosphorus, which 

 is abundant in all animal bodies. 



OEDER 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. 



Ml/a arenaria The Sand Mya. Plate V. fig. 4. 



Transversely ovate, rounded behind ; tooth very broad, 



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



tooth. 



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

 kinds generally live under sand or sludge, and the i)lace where they 

 lie is betrayed by a small hole, out of which they occasionally proti'ude 

 their siphon, which is placed at the posterior or ujiper 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 Cmnberland. This shell is well 

 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 procm'cd from the rivers in the counties of T;\Tone and 

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

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

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



* Priestley's Optics, page D67. 



