THE FRESH- WATER MUSSEL. 



89 



edge, which is nearly straight, is called the upper, or 

 dorsal border ; and the lower rounded edge is the 



Fig 89. 



Front End. 



Upper Edge of Mussel-Shell. 



lower, or ventral border. Then there are the two 

 sides — one on your right hand, and the other on your 



Fig. 90. 



The Four Straps. 



left; therefore one is named the right side, and the 

 other the left. So, when you pick up the half of a 

 MussEL-shell, you can always tell to which side it be- 



