TOOTHED WHALES 175 



there is reason to regard as ancient, there is often 

 greater difference between the component genera, 

 gaps having arisen through the extinction of certain 

 forms. 



The problem may therefore be approached by 

 endeavouring to ascertain which of existing Odonto- 



^5 *^ 



cetes is the older group or genus as the case may 

 be. 



Mr. Lydekker has recently described an exceedingly 

 interesting fossil from the Eocene of the Caucasus 

 under the name of Iniopsis caitcasica* This Cetacean 

 is represented only " by the hinder portion of a 

 cranium, and also by some fragments of jaws and 

 several vertebrae." But these remains, though not 

 abundant, seem to fix the systematic position of the 

 animal, of which they give such an incomplete idea, 

 and to prove that it should be relegated, as its name 

 denotes, to the neighbourhood of Inia, the fresh- 

 water dolphin of South America. In this extinct 

 animal and in Pontistes of the tertiaries of the 

 Argentine the maxillary bones are more deeply 

 excavated than in dolphins, and their posterior border 

 is squarely marked off and extends further back. 

 The lower jaw too of Iniopsis seems to have been 

 slender, and to have possessed very numerous teeth 

 as in the existing Platanistidae. These facts, though 

 few, seem to point to the great age of whales most 

 nearly allied to the existing Platanistidae. Now 

 whalebone whales do not go back so far into time. 



* " On Zeuglodont and other Cetaceous Remains from the Tertiary of 

 the Caucasus," Proc. Zool, Soc., 1892, p. 558. 



