186 



SUBKINGDOM VERTEBRATA. 



ORDER ELASMOBRANCHII. 



General Characteristics. The Strap-gilled fishes have 

 fixed gills and no gill-covers. Their skeleton is cartilagi- 

 nous ; skin, rough ; and the ventral fins are far back. In some 

 families the tail-lobes are of unequal length (JieterocercaT). 



Fig. 316. 



Fig. 317. 



Pastinaca hastata, Sting Ray. 



Raiidae. The Rays are noted for their enormous pec- 

 toral fins, formidable tail, and tesselated teeth. They some- 

 times weigh half a ton. The 

 teeth are adapted to crushing 

 sea-weed and shell-fish ; while 

 the tail, armed with hooked 

 spines, can be suddenly lashed 

 around an enemy, the barbs 

 frightfully lacerating the flesh.* 

 * Rhinobatidae (nosed-skate). 

 The Saw-fish has a sword-like 

 snout one-third the length of 

 Tesselated Teeth of a Say. t jj e body, and edged with tooth- 

 like spines. Brandishing this among a school of fishes, 

 many are at once disabled, and afterward eaten at leisure. 



* To this family belongs the famous Torpedo, which on being touched gives a 

 violent electric shock. It possesses a kind of voltaic pile composed of parallel 

 prisms, 1262 of which have been counted in a single fish. The electricity has been 

 used in galvanic experiments 1 as making a magnetic needle, etc. 



