3 84 ARCHAEROCEDE CHAP. 
slender rostrum and numerous teeth of the Platanistids and the 
squared excavations of the maxillaries. Argyrocetus patagonicus 
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 bones 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 Zarrhachis and Priscodelphinus, 
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. 
Sus-OrpErR 38. ARCHAEOCETI. 
This division of the Whale tribe embraces but a single family, 
Zeuglodontidae, of which but a single genus, Zewglodon, 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 
