1280 CLASS MAMMALIA. 



Mines, is represented solely by the genus Myrmecobius. In this re- 

 markable animal (fig. 1 149) the lower incisors are separated from 



Q 



one another, the cheek-teeth number -, of which the first three in 



9 

 either jaw are premolars ; while the molars have quadrangular multi- 

 cuspidate crowns, and are not well differentiated from the premolars. 

 Although some writers doubt the connection, it is probable that 

 Myrmecobius is the direct descendant of forms closely allied to 

 Amphilestes, of the Lower Jurassic of England ; the relations of the 

 two being perhaps somewhat similar to that existing between the 

 living Sphenodon of New Zealand, and the more specialised Hyper- 

 odapedon of the English Trias. 



Family Peramelid^e. — In this family, comprising the Bandicoots 



of Australia and New Guinea, the dental formula is I. J , C. -, 



3 I 



Pm. -, M. -, and the pes has two of the digits reduced and con- 



3 4 



nected by integument, as in the Macropodidce among the Diproto- 

 donts. Occasionally the canines have grooved or double roots. 

 Remains of existing species of Perameles and Peragale occur in the 

 Pleistocene of New South Wales. 



Family Didelphyid^e. — In all the members of this family the 



dental formula is I. -, C. -, Pm. -, M. -. The incisors are very 



4 13 4 



small and sharp ; the canines are large ; the premolars compressed ; 

 and the true molars constructed on the general plan of those of 



Fig. 1150. — Left lateral view of the dentition of Didelphys Azara> ; South America. *, In- 

 cisors; c, Canine; pm, Premolars; ?;«, True molars. The teeth marked pm 3 should be/;«4; 

 the teeth between these and/;/z 1 being pm 2. 



Dasyurus ; the lower ones having a blade and talon, with a distinct 

 inner cusp to the former. Each foot is furnished with five com- 

 plete digits ; and the humerus has an entepicondylar foramen. At 

 the present day the Opossums, as the members of this family are 

 commonly called, are confined to the New World, where they are 

 represented by the genera Didelphys (fig. 1150) and Chironectes ; 



