496 CLASS MAMMALIA. 



In a physiological point of view, these differences become 

 almost unimportant ; nor are they strictly grounded, in fact, 

 for the Common Seal has, in reality, an external conch, 

 very small, and hidden, it is true, but very distinct and 

 perfect. 



One organic distinction, of a general and influential cha- 

 racter, it is, however, now ascertained, does exist among 

 these animals ; and whether this alone will be found to 

 divide the whole of them into two sub-genera, or more 

 equally influential, will arise to furnish the foundations for 

 other sub-divisions, time and research must determine. 



The character alluded to is that of dentition. In the 

 Eats, we have had occasion to observe that the two leading 

 systems of dentition prevailing in these animals, seem to 

 separate the frugivorous from the remaining insectivorous 

 species ; and we shall have occasion to notice that the Mar- 

 supiata, which belong to the same order, are very de- 

 cidedly divided by the characters of the dentition of several 

 groups or sub-genera. So in the Phocae before us, some 

 have the cheek-teeth of a sharp, pointed, cutting character, 

 while others have them conical or obtuse. True it is, 

 that the external part of the cheek-teeth, however variously 

 destined, and however different in appearance, present, 

 when critically examined, rather an easy transition than a 

 positive change; the tubercles in the one case are more or 

 less developed, and more or less rounded or acute than they 

 are in the other. But in the points of difference, which 

 separate the two divisions of the Seals, now under consi- 

 deration, there is another material character in the root of 

 the cheek-teeth, inserted in the jaw. In the first division, 

 the root, or rather roots, are several; in the second, there 

 is but one, as in the cetaceous teeth. Hence, they may be 

 conveniently distinguished ; first, by having the cheek-teeth 

 with several tubercles, more or less indented, more or less 

 sharp or obtuse, but always with several roots : or, se- 



