VERTEBRATA. 
349 
Fig. 342.— Greenland Whale (Balcena mysticetus). North Atlantic. 
other Cetaceans teeth are developed, especially in Dol¬ 
phins and Porpoises ; but the Sperm Whale has them only 
in the lower jaw, and the Narwhal can show but a single 
tusk. The Dolphins are the only Mammals having no 
organ of smell. 
8. Sirenia resemble the Cetaceans in shape, but are close¬ 
ly allied to the hoofed animals in organization. They 
have the limbs of the Whales, and are aquatic; but they 
are herbivorous, and frequent great rivers and estuaries. 
They have two sets of teeth, the Cetaceans having but 
