106 POPULAR CONCHOLOGY. 



terior of the valves is often of a vivid green 

 colour, and raised in small blisters, which are 

 said to be formed by the accidental introduc- 

 tion of small particles of sand during the form- 

 ation of the nacrous fluid. 



Order III. 



MONOMYARI A. * 



Nearly the whole of the genera arranged 

 under this order and its families, attach them- 

 selves to rocks and other substances, not pos- 

 sessing the power of locomotion enjoyed by the 

 Dimyaria, still less that degree with which the 

 Univalves are endowed. They are more 

 limited in number than the Bivalves possessing 

 two muscular impressions, but there are among 

 them several well known, and to us useful 

 genera, as the Oyster, the Mussel, and the 

 Pearl Oyster. 



* Called sometimes Unimusculosa, the Latin form of 

 expressing the sense of Monomyaria. Les Conchiferes 

 monomyaires, Lamarck. 



