70 STUDIES OF ANIMAL LIFE. 



E. Inner Surface of the Shell. 



1. The hinge-teeth, irregular or blade-like projections 



near the dorsal margin. Of these the more ante- 

 rior are somewhat conical in shape and are called 

 cardinal teeth while the more posterior are blade- 

 like and are called lateral teeth. 



a. Compare the " teeth " of the right with those of 

 the left valve. 



J. What is the function of the hinge-teeth ? 



2. The anterior and posterior adductor muscle scars. 



These are markings near the dorsal margin. 



3. The pallial line. This extends from one muscle scar 



to the other. 



4. Draw the inner surface of the two valves, arranging 



them so that their dorsal margins are next to each 

 other. 



F. The Clam in the Open Shell. 



1. The mantle lobe, a flap covering the side of the body. 

 a. Determine whether it is the right or left lobe. 



h. Observe its thickened margin. 

 c. What is the relation of this margin to the paUial 

 line? 



2. The anterior and posterior adductor muscles. 



a. What is their relation to the muscle scars of the 



shell ? 

 h. What is the function of these muscles ? 



3. The siphons, openings on the posterior end of the 



clam marked by a fringe of short, dark tentacles. 

 (Dem.) 



Gr. Structures in the Mantle Cavity. 



The mantle cavity is the space between the mantle 

 lobes. 



