104 



Descriptive Zoology. 



the clam, it will be found that the mantle has several mus- 

 cular attachments. Running parallel to and not far from 

 the ventral margin is the mantle line, the line of attachment 

 of the inner edge of the muscular portion of the mantle. 



Anterior 



adductor 



muscle 



\ 



Cardinal 

 hinge 



Lateral hinge teeth 

 I 



Mantle line 



FIG. 63. INSIDE OF RIGHT VALVE OF CLAM SHELL. 



The Hinge Teeth. In most species of fresh-water clams 

 there are interlocking projections near the dorsal margin 

 of the valves. Near the anterior adductor are strong, 

 toothlike projections, the anterior, or cardinal, hinge teeth. 

 Parallel to the dorsal margin, near the hinge ligament, are 

 long ridges, the lateral or hinge teeth ; there are usually 

 two of these on one valve and one on the other, which fit 

 together when the shell is closed. These teeth aid in 

 keeping the shell shut. 



The Natural Position of the Clam. The ventral margin 

 is imbedded in the mud or sand, the anterior end usually 

 considerably deeper than the posterior. This position 

 brings the siphon openings above the mud ; but at 



