24 6 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



surface waters and feed on any other animals that they can 

 capture. The shark's mouth is on the underside of the head, 

 so it must turn over on its back in order to sieze any prey 

 that is swimming above it. The great basking sharks, genus 

 Cetorhinus, which reach a length of nearly forty feet, often 

 gather in numbers and float motionless on the surface of the 

 sea. The great white shark, Carcharodon carcharias, occurs 



FIG. 114. The common skate, Raja erinacca. (From Kingsley.) 



in all warm seas, and because it does not hesitate to attack 

 man it is often known as the man-eating shark. It attains a 

 length of thirty feet or more. The smooth dogfish shark, 

 Mustelus, the horned dogfish shark, Squalus, and the sand- 

 shark, Carcharias, often occur in great numbers in shallow 

 waters and do much damage by destroying lobsters and many 

 valuable food fishes. They are a great nuisance on the 



