384 ARCHAEOCETI 



slender rostrum and numerous teeth of the Platanistids and the 

 squared excavations of tlie maxillaries. Argyrocetus jiatagonicus 

 possessed also archaic characters, suggesting earlier affinities still. 

 The two condyles of the skull instead of being closely adpressed 

 to the skull stood out in a way more like that met with in 

 terrestrial mammals. The nasal hones instead of being abbreviated 

 rudiments are well developed as in the archaic Zeuglodonts. 

 The cervical vertebrae of this Whale are all perfectly free from 

 each other and individually long. The skull is on the whole 

 bilaterally symmetrical ; this again is a feature more pronounced 

 among the Platanistidae than among other Odontocetes. Accom- 

 panying these generalised Cetacean characters are some which 

 show that the animal was too specialised to be the direct ancestor 

 of any existing forms. The end of the mandible was upturned 

 and without teeth, its form being quite unique among Cetacea. 

 Other allied forms, such as Znrrhachis and PriscodelpMnus, 

 showed the same length of the cervical vertebrae. 



A very distinct family of extinct Whales is that of the 

 Squalodontidae. They to some extent bridge over the gap 

 between the existing Odontoceti and the Eocene Archaeoceti 

 (Zeuglodonts). 



The skull of these Whales was on the whole Dolphin-like. 

 But they possessed teeth which were distinctly specialised into 

 incisors, canines, and molars. The molars have a coarsely-serrated 

 cutting edge as in the Zeuglodonts, and are also to some extent 

 two-rooted. But they are more numerous, and so far approximate 

 to the conditions which characterise the more typical modern 

 Odontocetes. Squalodon was a long-beaked form, and Prosqualodon 

 had a skull whose proportions are nearer those of Kogia. 



Sub-Order 3. AECHAEOGETI. 



This division of the ^\''hale tribe embraces but a single family, 

 Zeuglodontidae, of which but a single genus, Zeuglodon, can with 

 certainty be discriminated. 



Zeuglodon is an Eocene form of large size, with teeth which 

 are limited in number and disposed in three series as incisors, 

 canines, and molars. The molars are double-rooted, a fact which 

 has given to the genus its name. The nasal bones being long 



