VERTEBRATA: MAMMALIA. 691 



Fam. 4. Rhynchoceti. This family is allied to the Cachalots 

 or Sperm Whales, and includes the so-called " Ziphioid Whales." 

 They are distinguished by the possession of a pointed snout 

 (the "beak" or "rostrum"), single blow-hole, small dorsal 

 fin, and dentition. The upper jaw is greatly extended and is 

 edentulous, any teeth which may be present not cutting the 

 gum. The lower jaw, on the other hand, possesses usually a 

 single pair of teeth, sometimes two pairs, which are sometimes 

 tusk-like, but which in other cases are concealed by the gum, 

 and are always most conspicuous in the males. 



The rostrum of these Cetaceans is of great density, and has 

 often been preserved in a fossil state, usually presenting itself 

 as a bony cylinder or elongated cone, generally more or less 

 water-worn. The most important living genera are Hyperoodon 

 and Ziphius, of which the former is found in the North Atlantic, 

 and the latter in the Mediterranean and South Atlantic. The 

 genera Berardius and Mesoplodon belong to the New Zealand 

 province, species of the latter having been obtained at the 

 Cape of Good Hope and on the coasts of Britain and France. 



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

 from all existing Odontoceti in the possession of molar teeth 

 implanted by two distinct fangs. Incisor teeth are likewise 

 present, and the animal is diphyodont The Zeuglodonts are 

 entirely extinct, and they are exclusively confined to the 

 Eocene, Miocene, and Pliocene periods. The chief genera 

 are Zeuglodon and Squalodon. 



Zeuglodon (fig. 387) is distinguished by its elongated snout, 



Fig. 387. Znuglodon cetoides. A, Molar tooth, natural size ; B, Vertebra, reduced. 

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



conical incisors, and molar teeth with triangular serrated 

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



