286 CHARACTERS OF VERTEBRATE ANIMALS 



British seas, but cannot be considered as a native species, its 

 habitat being the warmer parts of the ocean in almost all parts 

 of the world. 



2. Porbeagles. This includes sharks, which are most abun- 

 dant in the open ocean and are often of very large size. The 

 pointed teeth are large and strong, and the gill-slits are usually 

 very wide, while the spiracle is small or even absent. The 

 Porbeagle (Lamna cornubicd] is a North Atlantic form and fairly 

 common on British coasts. It is about 10 feet long. The 

 Thresher or Fox- Shark (Alopecias vulpes] is distinguished by the 

 remarkable length of the upper lobe of the tail. It is abundant 

 in the Atlantic and is the commonest large shark occurring on 

 our coasts, but is also well-known in the Mediterranean, its range 

 also including the coasts of California and New Zealand. The 

 Basking- Shark (Selache maxima) of the North Atlantic may 

 reach a length of over 30 feet. It is not uncommon on our 

 western coasts. Unlike the last-named species, which does not 

 attack man, the huge Rondeletian Shark (Carcharodon Rondeletii\ 

 which may attain the length of 40 feet, is universally dreaded. It is 

 found in the warmer parts of the open sea in all parts of the world. 



3. Dog-Fishes. Of this the Spotted Dog- Fish, selected as 

 our type (pp. 257-264), is a typical member. All are coast- 

 fishes, found in most tropical and temperate seas. Another British 

 species, closely resembling the preceding but of much larger size, 

 is the Nurse Hound (Scy Ilium catulus). The Zebra Shark 

 (Stegostoma tigrinum), common in the Indian Ocean, is a member 

 of this family. It may be as much as 15 feet long, and receives 

 its name from the characters of its markings, which consist of dark 

 transverse bands on a yellowish ground. 



4. Spiny Dog-Fishes. The species belonging here are mostly 

 of small size and are devoid of an anal fin. The gill-slits are 

 small and a spiracle is present. The Piked Dog- Fish (Acanthias 

 vulgaris] is common on the British coasts, and is characterized 

 by the presence of a sharp spine in front of each dorsal fin. A 

 much larger species is the Greenland Shark (Lcemargus borealis\ 

 which inhabits the seas of the Arctic region, and is one of the 

 worst enemies of the Greenland Whale, from the tail of which 

 it bites large pieces. It sometimes strays as far south as Britain, 

 and, though it may be as much as 1 5 feet long, is harmless to man. 



5. Angel-Fishes. This contains a single species, the Angel- or 



