XVII ELASMOBRANCHII — SELACHII 455 



The more typical representatives of this family are the Spiny 

 Dog-Fishes, which are distinguished by the presence of a strong 

 spine in front of each dorsal fin. They are more abundant in 

 temperate regions than in the intervening tropics. The more 

 important genera are AcantMas,Ce7itri'na,Centroj>horus,Spinax,a,iid 

 Centroscylliuvi. Acanthias vulgaris, the Picked or Piked Dog- 

 Fish, is a gregarious, voracious Shark, about 3 to 4 feet in 

 length, and is frequently seen in huge shoals all round the 

 British coasts, especially during the summer months. It is very 

 destructive to food Fishes, and its ravages result in serious loss 

 to fishermen. Acanthias is viviparous. Ce^itrina salviani is a 

 much smaller Shark, which frequents the Mediterranean and the 

 Bay of Biscay ; on rare occasions it has been taken off the 

 southern coast of England. Centropliorus occurs in deep water 

 in the Mediterranean and adjacent portions of the Atlantic, and 

 off the coasts of Japan. Centj-oscyllium is found on opposite 

 sides of the North Atlantic (Greenland and Massachusetts), and 

 in the opposite hemisphere at the Falkland Isles. A deep-water 

 form. Far acentroscy Ilium, has been obtained in the Bay of Bengal 

 at depths from 285 to 405 fathoms.^ 



Three remaining genera {Scymnus, Laeraargus, and Hchino- 

 rhinus) differ from the preceding in the absence of dorsal spines. 

 Scymnus lichia is common in the Mediterranean and the neigh- 

 boi^ring parts of the Atlantic. The Greenland Shark {Laemargus 



Fig. 260. — The Greenland Shark (Laemargus honalis). (From Goode and Bean.) 



lorealis) (Fig. 260) is an inhabitant of the Arctic regions, wander- 

 ing as far southwards on opposite sides of the Atlantic as 

 the French coast and Cape Cod. It is a huge, clumsy shark, 

 reaching a length of 26 feet. Numerous instances are recorded 

 of its capture off the coasts of Great Britain, especially in northern 

 waters. The Greenland Shark is said to be a determined foe to 



1 Alcock, Ann. Mag. Nat. Hist. (6), iv. 1889, p. 379. 



