SPOTTED OSTRACION. 141 



on many of the rays, the small, but rough and very 

 hard points on the skin of the sharks, which both 

 afford a substitute for the file of the cabinet-maker, 

 and, when polished, exhibit a beautiful material 

 often made use of in various neat articles of every- 

 day utility. To these, also, may perhaps be added, 

 the calcareo-comeous spines of the Diodons and 

 Tetraodons, which are placed with compai*ative 

 regularity, and, from their strength and hardness, 

 and the sharpness of their points, must be a species 

 of defensive organ most efficient. 



