FRESH-WATER MUSSELS. 



35 



mussel, it is necessary to pass a sharp blade between 

 the valves, and cut through the muscles, before the valves 

 will open. These muscles are called the adductor muscles, 

 and the scars or impressions on the valves are called the 

 adductor muscular impressions. Yery close to the adductor 

 muscular impressions are seen smaller impressions, and these 

 indicate where the muscles are attached which move the 

 foot. These muscles are called the pedal muscles, and the 

 impressions are called the pedal muscular impressions. One 

 occurs just behind the anterior adductor impression ; the 

 other will be found just above, and in front of the posterior 

 adductor impression. 



FIG. 39. THE EIGHT VALVE OP A FRESH- WATER MUSSEL. c, Cardinal Teeth ; Z, Lateral Tooth ; 

 li, Ligament ; a, Anterior Adductor Impression ; pa, Posterior Adductor Impression ; 

 ap, Anterior Pedal Muscular Impression; pp, Posterior Pedal Muscular Impression; 

 p, Pallial Line. 



34. Besides these marks, the pupil will see a delicate 

 and slightly irregular line running from the anterior to the 



