378 PALEONTOLOGY. 



anterior teeth have subcompressed, conical, slightly-recurved, 

 sharp-pointed crowns, and are implanted by a single root ; 

 the posterior teeth are larger, with more compressed and 

 longitudinally extended crowns (fig. 136), conical, but with a 

 more obtuse point, and with both front and hind borders 

 strongly notched or serrated. The crown is contracted from 

 side to side in the middle of its base, so as to give its trans- 

 verse section an hour-glass form (fig. 137), and the opposite 



wide longitu- 

 dinal grooves 

 which produce 

 this form be- 

 come deeper as 

 the crown ap- 

 ^^BS^ proaches the 



Fi s- 137 - socket, where 



Transverse section of a tooth of the Zeuglodon. Nat. size. ,-, , -■ 



divide the root into two fangs. The name Zeuglodon (yoke- 

 tooth) refers to this structure. The mode of succession of 

 the teeth in this genus conforms to the general mammalian 

 type more than does that of any of the existing carnivorous 

 Cetaceans. In the figure given by Dr. Carus* of a portion of 

 the jaw of Zeuglodon cetoides, a deciduous molar (fig. 136, a) 

 is about to be displaced and succeeded, vertically, by a second 

 larger molar. This mode of succession is not known in the 

 Platanista or Inia, which among existing true Cetacea present 

 teeth most like those of Zeuglodon ; but it is a mode of suc- 

 cession and displacement affecting certain teeth in the her- 

 bivorous Cetacea, or Sirenia ; and we thus seem to have in the 

 Zeuglodon another of those numerous instances of a more gene- 

 ralized character of organization in older tertiary Mammalia. 

 In systematic characters, Zeuglodon typifies a distinct family 

 or group, intermediate between Cetacea proper and Sirenia. 



* Nova Acta Cses. Loop. Carol., vol. xxii., tab. xxxix. B, fig. 2, p. 340. 



