4 SYSTEMATIC PALEONTOLOGY 



described in the following pages rendered impossible a complete re- 

 vision of the forms. All that has been attempted is to place the known 

 material in the most available form. 



The classification of the Cetacea is in a very unsettled condition so 

 that no one scheme can be said to be the correct one. The scheme 

 here given follows that of Flower and Lydekker." 



Suborder ARCHAEOCETl. 



Animals most nearly approaching the land-living ancestors of the 

 group; the skull elongate with well-developed nasal bones and the teeth 

 differentiated into an anterior, incisor series and a posterior, molar 

 series. These teeth, especially the molars, are extended in the antero- 

 posterior direction and have tuberculated cutting edges; the anterior 

 series is single-rooted and the posterior two-rooted. The body was 

 elongated and adapted to an aquatic life but the attachment of the 

 ribs, the structure of the palatal region and other portions of the body 

 are very seal-like in their relations. 



There is but a single family, the Zeuglodontidae, which is confined 

 to the Eocene formations. In the United States they are most abund- 

 antly found in the deposits of Alabama, Louisiana, and Mississippi. 



Suborder ODONTOCETI. 



Forms in which the skull has lost many of the typical mammalian 

 features retained in the previous suborder, especially in the facial 

 region; the external nares have retreated until they are simple openings 

 on the top of the head, descending almost vertically through the skull 

 just anterior to the front wall of the brain case. The retreat of the 

 nares has driven the nasal bones back until they are mere nodules in 

 the posterior wall of the upper portion of the nares. The nose is ex- 

 tended into a rostrum that may reach great length and slender propor- 

 tions; the teeth are variable, in some forms they are quite similar to 

 those of the preceding suborder, in others they are simple and conical; 

 either present in large number or reduced to a single tooth in each 

 half of the mandible. The vertebrae in the neck are, in the most 



1 Mammals Living and Extinct. Flower and Lydekker. London, 1890. 



