125 



by age of a great substance, and very unequal; tlu- 

 superior valve of some species shifting its place as the 

 animal requires more room, and producing a long beak 

 on the lower valve, similar to that of the Spondylus. 

 Hinge without teeth, ligament half internal, substance 

 of the shell lamellar, presenting a scaly or foliaceous ap- 

 pearance on the exterior; apices distant, the lower one 

 never recurved above the upper, as in the Gryphaea, 

 and Spondyli; interior of the valves pearly, and some 

 species produce small pearls, but of little value or 

 beauty. 



The Ostreae appear to have the faculty of removing 

 from one spot to another under particular circumstances. 

 They however almost always remain fixed and immove- 

 able in one spot, and exhibit no other signs of life than 

 that of opening their valves to receive the nutriment af- 

 forded them by the sea. 



The singular faculty possessed by this genus, as well 

 as by that of the Spondylus, of displacing the upper valve 

 as the shell increases in size, is exclusively peculiar to 

 these two genera. 



Notwithstanding the teeth of the hinge in the 



