148 FIRST LESSONS IN ZOOLOGY. 



rhomboidal, owing to the great development of the pectoral 

 fins. They swim close to the bottom, feeding upon shell- 

 fish, crabs, etc., crushing them with their powerful flattened 

 teeth. The smallest and most common skate of our north- 

 eastern Atlantic coast is Raja erinacea. It is one half of 

 a metre (twenty inches) in length, and the males are small- 

 er than the females. The largest species is the barndoor 

 skate, Raja Ice vis, which is over a metre (forty-two inches) 

 long. 



The sharks have from the earliest geological ages (the 

 Silurian) remained the masters of the sea ; even now 

 there are species as big as whales, the great basking shark 

 being from thirty to forty feet in length, and the Ehino- 

 don over fifty. They need little protection beyond spines, 

 as in the sting ray and the dog-fish, etc., the exception 

 being the torpedo, a slothful ray which lies half buried 

 in the sand, and with its electrical battery strikes dumb 

 any intruder. 



