VERTEBRATA 109 



External nostrils at base of muzzle ; tem- 

 poral fossse short, lateral ; no teeth, 

 but transverse horny laminte on the 

 upper jaw; Mysticeli. 



Fig. 44. — Zeuglodon cetoides Owen ; skull, much reduced. Prom Eocene of 

 Alabama. From Gaudry. 



The Archseoceti are few in number, and are chiefly repre- 

 sented by the gigantic Zeuglodon (Fig. 44.) They are not 

 known before or after the Eocene system, nor out of the 

 geographical area of the Northern Hemisphere. The 

 Odontoceti first appear in the older Neocene, and the oldest 

 family, the Squalodontidse, have the posterior teeth two- 

 rooted, as in the Zeuglodons. The other families with one- 

 rooted teeth were contemporary with them, and are repre- 

 sented in the present seas by numerous types, as the dol- 

 phins, sperm whales, etc. The Mysticeti, or whalebone 

 whales, appear in the Lower Neocene, and are still abun- 

 dant. They include the largest vertebrates. (Fig. 45.) 



The Odontoceti and Mysticeti are probably independent 

 descendents of the Archseoceti. The former retain their 

 dental and rib.characters, but the nasal bones are more ab- 

 breviated than in the Mysticeti. In certain Mysticeti of the 

 Neocene the frontals as well as the nasals are somewhat 

 elongate, and some (e. g., Cephalotropis) have temporal 

 ridges. 



SiEENiA first appear in a very generalized family in the 

 Eocene beds of some West Indian Islands. In the Neo- 

 cene of Europe and North America forms approaching 

 more nearly to the existing types are not rare, especially 



