]40 



SPOTTED OSTRACION. 



Ostradon cubicus, BLOCH. 



PLATE XV. 



WILL illustrate this form. In the small group of 

 fishes which have received the title of Ostracion, 

 the covering is remarkably hard, and is composed of 

 numerous pieces or compartments joined with the 

 greatest regularity, and often with a mathematical- 

 like precision in hexagonal plates. This covering 

 is discontinued at the tail, which is free for a short 

 space, and shows the necessity for this organ to be 

 placed so as to be capable of voluntary action. The 

 Spotted Ostracion is not an uncommon fish in the 

 Indian seas, and is said sometimes to reach a foot 

 in length. In the Isle of France it is esteemed for 

 its flesh, and is kept in artificial ponds, where it 

 becomes tame and familiar. 



Besides these forms of the skin, there is exem- 

 plified in many cartilaginous fishes a peculiarity in 

 the existence of the tubercules, usually pointed, 

 $nd having some resemblance to scales, but more 

 or less perfectly osseous, and are implanted deep to 

 adhere firmly. To this form belongs the tubercules 



