"At either end of the shell, just below the termination of the lateral 

 and cardinal teeth, there is a large, rounded scar which shows where the 

 adductor muscles of the animal are attached, and are therefore called 

 respectively the anterior and posterior adductor muscle scars. Not far 

 from these, two other scars are placed, which show where the anterior 

 and posterior foot retractor muscles are attached. 



" The ligament and the adductor muscles are two of the most im- 

 portant factors in the economy of the clam, governing as they do the 

 opening and closing of the shell. The adductor muscles by their con- 

 traction serve to keep the two valves closed, while the ligament, which 

 acts as a spring, tends to keep the valves open, the cardinal and lateral 

 teeth guiding the two valves, and keeping them from getting twisted. 



" If we were to cut a section through the living animal, we would see 

 that the two shells form a double lever, with the teeth as a fulcrum. 

 The ligament acts upon the short arm of the lever, the unibones, as a 

 spring which is constantly pulling the valves apart. The adductor mus- 

 cles, on the other hand, act upon the long arms of the lever, and by their 



contraction pull the valves together. It will readily 

 be seen that when the shell is tightly closed, the 

 animal is not at rest, because this causes some effort 

 on the part of the adductor muscles. The real 

 period of rest is when the shells are slightly gaping, 

 as they are when the animal is partly buried in 

 the mud. 



" The hollow in the upper part of the shell 



of clam shell, showing formed by the umbo is called the cavity of the 



beaks : in this are a number of small scars show- 

 ing where the muscles are attached which hold the 

 animal to the dorsal part of the shell. 



" About a quarter of an inch from the edge, an 

 impressed line runs parallel with the ventral mar- 

 gin of the shell. This shows where the mantle of 

 the animal is attached. It is called the pallial line, 

 and extends in an unbroken line from one adductor 

 muscle scar to the other. The interior of the whole shell is pearly 

 and iridescent." 



Having completed our examination of the shells, and feeling thor- 

 oughly rested, we all followed Harry's example by taking off our shoes 

 and stockings, rolling up our trousers, and wading into the lake after 

 clams. Buried in the muddy sand, they were all about us, and in all 

 conceivable angles. Here and there several individuals were crawling, 



method of opening and 

 closing the valves. I., 

 ligament ; II., III., the 

 umbones; IV., V., lateral 

 teeth in the left valve 

 VI., lateral tooth in the 

 right valve ; VII., VIII., 



muscle ; X., XI., ventral 

 surface of shell, or long 

 arms of the lever. (After 

 Lancaster.) 



