60 THRESHER, BLUE-SHARK, PORBEAGLE, DOG-FISH. 



length of from ten to twelve feet. Its gape is not so wide, nor 

 are its teeth so formidable in proportion to its size, as those of 

 the preceding ; but its tail is a powerful weapon, and it is 

 exceedingly bold and voracious in its disposition. It has been 

 stated on good authority, that it is not uncommon for a Thresher 

 to approach a herd of Dolphins which may be sporting in unsus- 

 picious security, and by one splash of its tail to put them all to 

 flight, like so many hares before a hound ; yet the Dolphin is 

 six times the bulk of the Thresher. The Biw-shark bears more 

 resemblance to the "White in its general form, but is much smaller, 

 not exceeding six or seven feet in length. It is very common off 

 the Cornish coast, and is extremely troublesome to the fishermen 

 during the Pilchard-fishing season, cutting their lines and nets, 

 and devouring the fish. The Porbeagle belongs to an allied 

 genus, Lamna, which differs from the true Sharks in having a 

 pyramidal snout, and the gill-openings placed rather further for- 

 wards. Its common name seems to be compounded of Porpoise 

 and Beagle ; for it bears some resemblance to the former in 

 shape, whilst it corresponds with the latter in its habit of hunt- 

 ing in packs. It is occasionally met with on almost all parts of 

 the British coasts, being found chiefly in currents near rocky 

 places ; it is voracious in its habits, swallowing entire Fishes of 

 two feet in length. The Notidamus, which is an inhabitant of 

 the Mediterranean, is the largest of the true Fishes, its length 

 being sometimes as much as thirty-six feet ; but it is compara- 

 tively harmless. 



583. This family contains many other genera, more or less 

 departing from the ordinary type ; among these we may mention 

 the curious Zygcena or Hammer-headed Shark ; which resem- 

 bles the ordinary Sharks in the form of its body, but has its 

 snout prolonged into the form of a double-headed hammer, with 

 an eye in the middle of each extremity. It is occasionally met 

 with in European seas, attaining the length of twelve feet, 

 and larger ones are said to inhabit the tropical ocean. 

 The Dog-fish is nearly allied to the Sharks ; and is probably 

 more abundant on our own coast than any other of the order. 

 Almost every one who walks along the shore may meet with its 



