18 THE ELEMENTS 



Cicatrix, or Tongue, is the impres- 

 sion left on the inside of the valves, by 

 the adhering muscles of the animal 

 It differs in most shells, according to 

 the shape of the muscle, and is either 

 semi-ovate, round, lunate, elongated, 

 &c. It is often of great use in distin- 

 guishing a species ; being, with a very 

 few exceptions, alike in shells of the 

 same species. Some shells have only 

 one cicatrix, as the edible oyster, and 

 muscle ; others have two, and some 

 few more ; the Tellina Fusta for exam- 

 ple. Plate 1 st, figures 6 and 8, eeee. 



Lunule. The lunated depressions, 

 situated in the anterior and posterior 

 slopes. In different species of the 

 Venus they are prominent, character- 

 istic marks, often of much service in 

 ascertaining a species. Plate 1st. 

 fig. 4th, bb. 



Ligament perforation. The cir- 

 cular aperture, or perforation, through 

 which the ligament passes ; by which 



