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iv v J > -~ 



CHAPTER XIII: PORPOISES AND DOLPHINS. 



General features of Porpoises and Dolphins. Narwhal. 

 White Whale or Beluga. Killer Whale or Grampus. False 

 Killer Whale. Irawadi Dolphin. Risso's Dolphin. Pilot 

 Whale. 



Family Delphinidae. 



The family Delphinidae includes those Cetaceans popularly 

 referred to as Dolphins and Porpoises ; creatures of relatively 

 small or moderate size, usually but not invariably having a 

 dorsal fin about the middle of the back, and also, but again not 

 invariably, possessing functional teeth in upper and lower jaws. 

 The normal range in size is from 5 to 14 feet, but included in 

 the family are some rather larger species which, although quite 

 typical dolphins.have been dignified by the name of " whale ". 

 Thus we have the Killer Whale, the False Killer Whale, the 

 White Whale, the Pilot Whale — all of them true dolphins. 



A single crescentic blowhole situated well back from the 

 tip of the snout and having its concave margin forward is 

 found in all members of the family. Many structural features 

 distinguish the family ; the absence of whalebone in the 

 mouth separates its members at once from the Mystacoceti or 

 Whalebone Whales, and of crests on the skull from the Beaked 

 and Sperm Whales. From the River Dolphins the family 

 Delphinidae is distinguished by having only 4 or 5 pairs of 

 double-headed ribs, whereas the former have 8 pairs. 



