THE CETACEA, OR WHALES. 251 



appeared. That the Whalebone whales are geologi- 

 cally younger than the smooth whales is likewise 

 proved by their generic characters, the furrow which 

 extends from the throat to the belly, and the 

 humped or fin-shaped protuberance on the back. 

 Hence not only does the preserved skull of one of the 

 most important group of the Whalebone whales 

 (the Cetotherium) oblige us to maintain the animal 

 to have been one of the smooth wlmles, but we are 

 also enabled, from this circumstance and the geo- 

 logical period, to conclude that these whales did not 

 possess either furrows on their breast or fins on 

 their back. 



The time of the fullest development of the 

 Cetacea belongs to the Miocene period, when they 

 had associates in the large and also numerous small 

 Whalebone whales, for instance, the Cetotherium 

 just mentioned, which is closely related to the 

 present Bearded or Whalebone whales (from two to 

 ten feet long), and also the Dolphins and the Zeu- 

 glodonta. The last-mentioned group is formed of 

 the two entirely extinct genera, Zeuglodon and 

 Squalodon. 



Brandt has in detail urged it as improbable 

 that Zeuglodon, as is often supposed, can be 

 regarded as an intermediate form between the 



