NATURAL HISTORY. 455 



The THORNBACK SKATE derives its name from the spiny 

 armature of the tail, with which the fish defends itself most 

 vigourously by bending itself almost into a semicircle and lash- 

 ing about with its tail. The female of the Thornback Skate is 

 termed a Maid. It often attains to a large size, the largest 

 known being twelve feet in length, and nearly ten in width. 



The jaws of the Rays are exceedingly powerful, and enable 

 them to crush with perfect ease the various shell-fish on which 

 they feed. 



The STING RAY is another species, which is armed with a 

 serrated bone in its tail, with which it can inflict painful and 

 even dangerous wounds. 



Sub-order III. CYCLOSTOJVII. (Gr. KvK^oh a Circle ; crt/m, tlio mouth.) 

 Family I Petromyzonidie. (Gr. Uerpog, a Stone; /i.v&, I suck.) 



PETKOMYZOX. 



Marinas (Lat. Marine), 7te Lamprey. 



These curious fishes, in many respects the lowest in organiza- 

 tion of the vertebrate animals, are chiefly remarkable for the sin- 

 gular construction of the mouth, which, formed like that of the 

 leech, enables it to hold firmly to any object by suction. The 

 breathing apparatus appears externally to consist of fourteen 

 small apertures, seven on each side of the neck. Their progress 

 through the water is accomplished by a rapid undulating move- 

 ment. 



