THE CARTILAGINOUS FISHES 215 



probability the ancestors of most, if not all, the existing types of 

 fishes. They are distinguished by having a gristly internal skeleton, 

 which in some cases is partly calcified, while the exo-skeleton is 

 formed of " shagreen " or tooth-like scales termed " dermal teeth." 



The Elasmobranchs are usually large fishes; none of them is 

 very small, while some of the sharks are huge creatures, the largest 

 of all living fishes. They inhabit almost all seas, the largest species 

 being found in the tropics ; they are numerous in temperate waters, 

 while a few species frequent the Arctic region. Many are surface 

 dwellers ; others live at the sea-bottom at varying depths to 

 nearly a thousand fathoms. They are typically marine creatures, 

 but will sometimes ascend rivers, and a few species are dwellers 

 in fresh water. 



The sub-order Selachii includes all modern Sharks and Dog- 

 fishes Dog-fishes being only a small variety of shark. They are 

 all fierce, active creatures, generally of roving disposition, rang- 

 ing the surface of the sea, and waging constant warfare on all other 

 denizens of the deep. They are very voracious and, with one 

 or .two exceptions, carnivorous, their food ranging from molluscs, 

 crustaceans, or sometimes even plankton, to fishes of all sizes ; 

 while many species attack and kill whales, and, as is only too 

 well known, will even devour man should he come within reach of 

 their cruel jaws. 



The Shark family are distinguished by their great muscular 

 strength and their strong, toothed jaws. The head is somewhat 

 shovel-shaped, and the mouth, as a rule, is on the under side. The 

 teeth may be blunt and crowded together into great pavements 

 used for crushing food, or sharply pointed and saw-like for rend- 

 ing and tearing. When the latter is the case the sharp teeth, 

 as they are worn down by constant use, are shed and replaced by 

 new ones. 



The Great White Shark (Carcharodon rondeletii) is one of the 

 largest and most formidable of these dangerous fishes. It frequents 

 the warm tropical and subtropical seas, from the Mediterranean to 

 Australia and New Zealand, and but rarely comes within sight 

 of the British coast. In colour it is an ashen grey above and white 

 below, and it is said occasionally to attain a length of 40 feet, 

 but the more usual size is from 20 to 30 feet. It is a great wanderer, 

 and swims with remarkable swiftness and ease, and will follow the 



