390 MARSUPIALS. 



the absence of the upper canines as functional teeth ; the germs, 

 however, of these teeth are always to be found in the young 

 mammary foetus of the Macropus major, and I have seen them 

 present, but of very small size, and concealed by the gum, in the 

 adults of some small species of Kangaroos, as Macropus rujlventer, 

 Ogilby, and Macr. psilopus, Gould. This, however, is a rare ex- 

 ception ; while the constant presence and conspicuous size of the 

 canines will always serve to distinguish the Potoroo from the Kanga- 

 roo. But there are also other differences in the form and pro- 

 portions of certain teeth. The upper incisors of the Kangaroo have 

 their cutting margins in the same line, the anterior ones not being 

 produced beyond that line, as in the Potoroos : the third or 

 external incisor is also broader in the Kangaroos, and is grooved 

 and complicated by one or two folds of the enamel, continued from 

 the outer side of the tooth obliquely forward and inward. In most 

 species the anterior fold is represented by a simple groove : the 

 relative size of the outer incisor, the extent and position of the 

 posterior fold of enamel, and consequently the proportions of the 

 part of the tooth in front or behind it, vary more or less in every 

 species of Macropus : there are two folds of enamel near the anterior 

 part of the tooth in Macr. major, and the posterior portion is of 

 the greatest extent, and the entire crown of the tooth is relatively 

 broadest in this species. The middle incisor is here also compli- 

 cated by a posterior notch and an external groove. These modifica- 

 tions of the external incisors of the Kangaroos were first noticed by 

 M. Jourdan, and subgeneric distinctions, have been subsequently 

 based upon them. 



M. Fr. Cuvier has proposed a binary division of the genus 

 Macropus, as here defined, founded on the absence of permanent 

 spurious molars, and a supposed difference in the mode of succession 

 of the true molars in certain species of Kangaroo, combined with 

 modifications of the muzzle or upper lip, and of the tail. 



The dental formula which I have assigned to the genus Macropus 

 is restricted in its application by that Naturalist to some small 

 species of Kangaroo, grouped together under the term Halmaturus, 



