XXXIV INTRODUCTION. 



Shells that remain fixed by one of their valves, 

 such as oysters, or that occasionally attach them- 

 selves by their byssus, or threads, such as muscles, 

 are often found in the fissures of rocks ; while the 

 limpets, the sea ears, the acorn-shells, and some 

 other species of univalves, adhere firmly to the 

 surface. In warm climates, where the Mangrove, 

 and other trees, frequently grow within the influence 

 of the tide, it is not uncommon to find their roots 

 (and such of their branches as bend into the water) 

 loaded with oysters, acorn-shells, and such other 

 species as adhere to solid bodies. 



On the coasts where the bottom of the w^ater is 

 muddy, shells are indicated, by slimy strings rising 

 occasionally to the surface. To procure these shells 

 a French author directs us to use a small net with 

 fine meshes, mounted on a hoop of iron, and fixed to 

 a pole of sufficient length. This is to be plunged to 

 the bottom, directly under the place where the 

 shell is supposed to lie, and, when drawn up, the 

 mud escapes through the meshes, and leaves the shell 

 in the net. 



All that has been hitherto said applies only to 

 shells that inhabit the banks of the sea, or at least 

 a very little distance from its shore. There are many, 

 on the contrary, such as the Cones, the Olives, the 

 Cowries, the Volutes, and the larger species of 



