56 Practical Zoology. 



hard covering and the ability to shut it so tightly and remain shut 

 so long? 



EXTERNAL FEATURES OF THE CLAM SHELL. 



If a live clam is used, place it on a plate, or in the dissecting pan. 



1 . Notice the two parts of the shell, the valves. 



2. The edge along which the shell opens is the ventral margin. 



3. The edge by which the two valves join each other is the 

 dorsal margin, or hinge margin. 



4. The concentric lines parallel to the ventral margin are the 

 lines of growth. 



5. The raised point around which these lines center is the beak, 

 or umbo. The umboes are nearer the front, or anterior, end of 

 the clam. 



6. Toward the posterior end, back of the umboes, between 

 the valves, and uniting them, is the hinge ligament. 



7. Hold the closed shell with the hinge margin uppermost, the 

 hinge ligament nearer, and the umboes pointing away from you. 



The end pointing from you is the anterior end. 



The end pointing toward you is the posterior end. 



The upper edge is the dorsal margin. 



The lower edge is the ventral margin. 



The half-shell to your right is the right valve. 



The half-shell to your left is the left valve. 



Fix these relations firmly in mind. 



8. Make a drawing of the clam as seen from the left side, 

 naming all the parts. 



9. Observe the color, the degree of cleanness, and general 

 condition of the different parts of the shell, and consider the 

 relations between these facts and the position of the clam when 

 first found. 



DISSECTION OF THE CLAM. 



How to open a Clam. It is difficult for beginners to open 

 clams without mutilating the soft parts. It is better to have them 

 opened by the teacher. If any student is following these direc- 



