20. 



POPULAR COXCHOLOGY. 



of terms have been adopted to mark the variations which 

 occur. A is the apex, B the mouth or aperture, which in 

 fig 2. is entire; in fig. 3. notched ; in fig. 4. channelled. 

 D is the spire, formed of a greater or less number of whorls, 

 the intersections of which, or where they wrap over, are 

 called sutures E. F is the right or outer lip ; G, the left, 

 inner, or columella lip ; H, in fig. 3., is the notch; I, in 

 fig. 4., is the channel or canal ; K, in figs. 5 and 6., the 

 umbilicus ; L, in fig. 7., is the columella, or pillar, which 

 can only be seen when the shell is cut open ; m are the 

 plaits on the left lip of fig. 3. The lower part of the 

 aperture of a shell is in reality the anterior or fore part, 

 for it is there that the head of the animal protrudes ; but 

 it is generally called the base ; the entire edge, when the 

 lips are not separated by a notch or canal, is called the 

 peretreme. 



The component parts of a bivalve shell will be under- 

 stood by referring to 

 the annexed represent- 

 ation, in which A A 

 are the bosses, or pro- 

 minences, which exist 

 near B, the hinge, or 

 juncture of the two 

 valves ; the latter are 

 also kept together by 

 strong muscles, which proceed from the animal itself, and 

 are attached to each valve on the interior surface, where 

 they leave a scar when removed. Under the bosses, and 

 inside the valves, are the teeth, being little projections that 

 lock into each other, and serve to keep the valves steady 

 when closed ; they are divided into cardinal*, or principal 



Bivalve shells. 



* From cardo, Lat., a hinge. 



