264 MOLLUSCA 



(14) The Hinge Ligament. The anterior end of the shell is 



blunter than the posterior, the dorsal is thicker than 

 the ventral. Identify the hinge ligament dorsally 

 between the valves. 



(a) Color? 



(b) Structure? 



(c) Use? 



(15) Sketch one valve externally and indicate all the 



points so far made out. 

 2. The Shell internally. 



(1) Color? 



(2) Structure? 



(3) Surface? 



(4) Any pearls? Theory of the formation of pearls? 



(5) Any lines? 



(6) Teeth of the shell. 



(a) How many in right valve? In left? 



(b) Use of these teeth? 



(7) Muscle scars. 



(a) How many? 



(b) Where are they found? 



(c) Use? By what muscles? 



(8) Sketch inside of the shell and indicate all markings. 



B. Internal Morphology 



Kill the clam in water gradually heated to about 140° F. The 

 muscles relax, the foot protrudes, and the clam is easily exposed 

 to view for study. The clam may be killed by inserting a strong 

 knife between the valves near the anterior end of the shell and 

 severing the muscles which hold the shell closed. 



1. The Clam inside the shell. 



(1) The mantle is found covering the body and adhering to 



the valves of the shell. Separate the mantle from 

 one valve by inserting a scalpel between them. 



(a) Shape? 



(b) Attachment? 



(c) Use? 



(2) The gills are leaf-like organs under the mantle. 



