1284 CLASS MAMMALIA. 



scalpriform, and grow from persistent pulps. The fore and hind 

 limbs are of approximately equal length, and adapted solely for 

 walking ; the humerus has no foramen ; and it is probable that the 

 covering of the toes approximated to the nature of hoofs. The 

 mandible, although more convex below, is not unlike that of Noto- 

 therium. Professor Huxley has named a second species on the 



155. — Left literal view of the skull oiDiprotodon Atistralis ; from the Pleistocene 

 of Australia. Much reduced. (After Owen.) 



evidence of premolars, but it is not certain that this determination 

 is correct. 



Family Phalangerid^e. — This family includes the existing 

 Phalangers and the Koala (Phascolarctus), as well as a remarkable 



-? 

 extinct genus. All these animals have /. -, and an upper and fre- 

 quently also a minute lower canine ; while the premolars may vary 

 from - to -, and the true molars from - to -. The structure of 



the cheek-teeth is subject to great variation in the different genera ; 

 the fourth premolar being either secant or tubercular. There is no 

 pit or perforation in the masseteric fossae of the mandible. The 

 limbs are of nearly equal length ; the manus has five subequal digits, 

 but the second and third digits of the pes are very slender and 

 partially united by integument ; and the hallux is always opposable. 

 In many of the true Phalangers the fourth premolar is grooved, and 

 the dentition closely resembles that of the existing genus Hypsi- 

 prymnodon among the Macropodidce. Of living genera the only one 



