181 



THE HETERODONS. 



LEAVING the large headed whales, we come now to 

 the second subdivision, which has been proposed by 

 Blainville, and adopted by Lesson and other systema- 

 tists. Besides having the head of the ordinary pro- 

 portion which, with other characters, distinguishes 

 it from the first subdivision, it is distinguished from 

 the third and last chiefly by the teeth. Whilst 

 this third is almost uniformly supplied with a great 

 number of teeth in both jaws, amounting sometimes 

 to hundreds, this second subdivision has generally a 

 very small number indeed, which are moreover very 

 heterogeneous, confined sometimes to the one jaw, 

 and sometimes, in other genera, to the other. Some- 

 limes, as in the narwhal, they are not within the 

 mouth at all ; and several genera are believed to be 

 even still more destitute of teeth. From this great 

 paucity, and also from their variety, Blainville has 

 denominated this subdivision heterodon (from srego$ 

 and ofos). It will be perceived that the character 

 is not a very striking, or perhaps even a very natural 

 and positive one : but, as we presume not to intro- 

 duce a new classification ourselves, we take it as we^ 

 find it, and follow it as far as it goes, because we 

 regard it useful. It includes the Narwhal or Sea 

 Unicorn, the Diodons or two-teethed whales, the 

 Hyperoodon of Cuvier, the Aodon or toothless whale, 

 and the Ziphius, which includes some of the most 

 important fossiles which have been discovered. 



