BIVALVE SHELLS. 31 



ORDER SECOND, 



BIVALVE SHELLS. 



Cenas 4— MYA, 

 Animal an Ascidia; shell bivalve, generally gaping at one end ; 

 'hinge with a broad, thick, strong, patulous tooth, seldom more 

 than one, and not inserted in the opposite valve. 



Ml/a Arenaria.— The Sand Mya. Plate V. fig. 4. Trans- 

 versely 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 pi-oboscis. 

 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 con. 

 siderable importance is, the quantity of pearls which they sometimes pro- 

 duce. As illustrative of tlie value of pearls produced by the Mya Margariti- 

 fera, (Unio Margaritifera, Lamarck) it may be mentioned that according to 

 Camden, Sir John Hawkins had a patent for fishing that shell in the river 

 Irt in Cumberland. This shell is well known in Britain, by the name of the 

 Pearl Muscle. We are informed in the philosophical transactions, that se- 

 veral pearls of great size have been procured from the rivers in the counties 

 of Tyrone 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 from the same places have sold from £i lOs., to 

 £10 each. One of the latter price was sold a second time to Lady Genlealy, 

 who had it placed in a necklace, and refused £80 for it, which she was of- 

 fered by the Countess of Ormond. There was also a great fishery for pearls 

 in the river Tay, which extended from Perth to Loch Tay ; and it is said 

 that the pearls sent from thence, from the year 1761 to r.64, were worth 

 £10,000. It is not uncommon in the present day, to find pearls in those 

 shells, which bring from £1 to £2. It is said that those in the Scottish 

 CrowTi which forms part of the regalia now exhibited in the Castle of Edin- 

 burgh, are the produce of the river Tay. 



GenMs5.— SOLEN. 



Animal an Ascidia ', shell bivalve, oblong, open at both ends ; 

 fiinge with a subulate reflected tooth, often double, and not in- 

 serted in the opposite vaxVd. 



Solen Siliqua. — The Pod Solen, Plate I. fig. 5. Shell linear, 

 straight ; in one valve two teeth, and one in the other, having a 

 lateral inclined tooth corresponding with the opposite lamina ; 

 covered by a fine olivaceous brown epidermis, very glossy, and 



