580 MANUAL OF ZOOLOGY. 



Fam. 5. Zeuglodontidcz. The members of this family differ 

 from all existing Odontoceti in the possession of molar teeth im- 

 planted by two distinct fangs. The Zeuglodonts are entirely 

 extinct, and they are exclusively confined to the Eocene, Mio- 

 cene, and Pliocene periods. The chief genera are Zenglodon 

 and Squalodon. 



Zeuglodon (fig. 248) is distinguished by its elongated snout, 

 conical incisors, and molar teeth with triangular serrated 

 crowns, implanted in the jaw by two roots. Each molar looks 



Fig. 248. Zeuglodon cetoides. A, Molar tooth, natural size ; B, Vertebra, reduced. 

 From the Middle Eocene of North America. (After Lyell ) 



as if it were composed of two separate teeth united on one side 

 by their crowns ; and it is this peculiarity which is expressed by 

 the generic name. The species of Zeuglodon are Eocene and 

 Miocene. The species of Squalodon are Miocene and Pliocene. 



CHAPTER LXXVII. 

 UNGULATA. 



ORDER VI. UNGULATA. The order of the Ungulata, or Hoofed 

 Quadrupeds, is one of the largest and most important of all the 

 divisions of the Mammalia. It comprises three entire old orders 

 namely, the Pachydermata, Solidungula, and Ruminantia. 



The first of these old divisions that of the Pachydermata 

 included the Elephants, Rhinoceros, Hippopotamus, Tapirs, 

 and the Pigs, all characterised, as the name implies, by their 

 thick integuments. The name is still used to express this fact, 

 though the order is now abandoned, and is merged with that 



