100 



SKETCH OF THE HISTORY OF MAMMALIA . 



scending ramus of the lower jaw is deeply emarginated 

 behind, and the posterior angle acute. Fig. 62 repre- 

 sents the skull of Octodon in different views ; and the 

 skull of an allied genus, Ctejiomys, is given in Fig. 65. 



Cuming's Octodon in size and shape resembles a 

 water-rat. General colour brownish gray clouded with 

 dusky black ; under surface dusky gray ; base of the tail 

 beneath nearly white. (Fig. 63.) 



— Teeth of Echymys. 



These animals are exceedingly abundant in the central 

 parts of Chile. They frequent by hundreds the hedge- 

 rows and thickets, where they make burrows which 

 communicate with one another. In the neighbourhood 

 of Valparaiso multitudes may be seen together feeding 

 fearlessly in the day-time. Sometimes they ascend the 

 lower branches of small shrubs, but not often. They 

 are very destructive to fields of young corn. On being dis- 



