CONCHIFERA OR BIVALVES. Ill 



verse, cylindrically oblong, equivalve, and co- 

 vered with a brown epidermis; extremities 

 round ; bosses scarcely prominent. The hinge 

 is straight ; ligament mostly internal. Animal, 

 foot tongue-shaped. 



The Lithodomus, when young, suspends itself 

 to rocks by a byssus*, but, as it grows, it 

 pierces a hole, and introduces itself, forming a 

 cavity which thenceforward it never leaves: 

 indeed, after a short time, as it merely enlarges 

 the interior, without making the entrance any 

 wider, its increasing bulk renders it unable to 

 quit its cell, and in these circumstances its 

 byssus dies away, being no longer necessary. 

 It is common in the Mediterranean and the 

 Antilles, where it often 

 pierces other shells. 



70. Mytilus. Shell lon- 

 gitudinal, equivalve, ham- 

 shaped, somewhat triangular, 

 bosses placed at the extreme 

 end, hinge mostly without 

 teeth ; fastened by a byssus : 



* This assertion is from Cuvier ; Sowerby thinks it 

 has no byssus. 



