ORDER BIT.IUSCULOSA. 83 



with those belonging to the last oi-tler, but as they pos- 

 sess two or more pairs of muscles, they are much more 

 capable of moving from place to place, and, consequently, 

 are seldom found in any great quantities in one spot, 

 and being found, as they generally are, in a consider- 

 able depth of water, they are not so easily obtained. 



The Fresh-Water Mussel, 

 (Ayiodonta cijgnoea.) 



Although this shell, and several other species which 

 nearly resemble it, are known by the trivial name of 

 Mussel, the only resemblance between them consists in 

 their outward appearance, the animals which inhabit the 

 shells being very distinct, both in organization and in 

 habits. The Mussels, as we have already said, have 

 very little power of moving from place to place, while, 

 on the other hand, the Anodonta is at times far from 

 being a sluggish animal, and, for the purpose of shifting 

 its position, it avails itself of a very strong and broad 

 muscular foot. The shell of the Anodonta is sometimes 

 found to contain pearls, a circumstance which frequently 

 occurs in all shells which are lined with mother-of-pearl. 



Some of the Scotch rivers have produced numerous 

 specimens of pearl, very large and beautiful, and which 

 used to bear an extremely high price. 



A paper in the Philosophical Transactions for 1693, 

 mentions the collection of pearls from this shell, in the 

 river Omagh, County Tyrone, in Ireland. " The poor 

 people," he says, "in the Summer months, go into the 

 water, and some with their toes, some with wooden tongs, 

 and some by putting a sharpened stick into the opening 

 of the shell, take them up ; and, although, by a common 

 estimate, not above one shell in a hundred may have 



