10 TERMS BIVALVES. 



Lateral teeth are situated on the sides of the 

 valves, and are generally long and flat, sometimes 

 hollow. Some hinges are straight, others curved. 

 Here is the hinge of Area, furnished with many 

 small teeth. (Plate 3, h.) 



" The ligameyit is a membrane that connects 

 the valves, and keeps the hinge in its proper 

 place : it is always situated near the beaks. The 

 ligament is very perceptible in the cockle, in 

 Pecten^ or scallop, in Tell'ina^ &c. 



'' The heahs are the most pointed parts of the 

 bivalve shell (Plate 3, c.) ; when the valves are 

 closed, the line where they meet is called the 

 seam. (Plate 3j g?.) 



'' The anterior slope is that part of the shell 

 where the ligament is placed, and is also called 

 the area. (Plate 3, e.) The posterior slope, or 

 areola^ is the other side of the beaks. (/.) 



" The lunula is a crescent-like depression on 

 either the area or areola. The edge of the valve 

 is called the margin ; it is often finely crenulated, 

 or toothed. The interior of the valve is called the 

 cavity, (g.) In the valves of this ark-shell here 

 are two broad marks, shining and glossy, (g.) In 

 those of the oyster and muscle that I now show 

 you, there is but one. These marks are muscular 

 impressions ; they are the parts where the muscles 

 of the animal have been affixed, and are termed 

 cicatrix. 



