CONCHIFERA OR BIVALVES. 127 



are inhabitants of salt water only, and are 

 always found on rocky^ ground, at no great 



depth from the shore, attached by the under 

 valve. The oyster, and indeed all bivalves 

 which adhere by the shell, are covered at their 

 birth with a mucilaginous liquid which attaches 

 them to the surface of any object on which 

 they rest. The animal strengthens this first 

 adhesion in the same manner that it increases 

 the size of its shell. At the mouths of several 

 American, African, and Indian rivers, great 

 quantities of oysters are found attached to the 

 roots of trees, and even to their branches, 

 where they are so situated as to be covered by 

 the tide. Mrs. Lee, in her « Stories of Strange 

 Lands" says, " The flavour of the tree-oyster is 



