746 MAMMALIA. 



sets are defined by the characters of the teeth, which are, of course, 

 adapted to habit. In the members of the first sub-order the incisors 



are numerous (not less than -), small, and almost equal in size ; while 



the canines are large, and the molars furnished with sharp cusps. The 

 whole dentition presents a striking resemblance to that of the Eutherian 

 Carnivores. To this group the name Polyprotodontia is applied, and 

 the forms included in it are typically carnivorous or insectivorous. The 

 caecum is absent or very small. 



In the remaining families the incisors are usually ^ in number, and 



those above are of unequal size, the centre ones being largest. The 

 canines are usually small or absent ; the molars are furnished with 

 blunt tubercles, or transverse ridges. To these typically herbivorous 

 forms the name Diprotodont is applied ; they are more highly special- 

 ised than the Polyprotodonts, and are more modern. 



A. POLYPROTODONTIA 



1. Family Didelphyidse. American opossums, distributed from the 



United States to Patagonia, arboreal in habit, usually carnivorous 

 or insectivorous in diet. The limbs have five clawed digits ; 

 the hallux is opposable. The tail is generally long, and often 

 prehensile. The stomach is simple ; the coecum small. The 

 pouch is generally absent, but the young are often carried on 

 the back of the mother, their tails coiled round hers. Dentition, 

 5134. 



Examples. The Virginian or crab-eating opossum (Didelphys 

 marsupialis}) with a pouch ; the woolly opossum (D. lanigera] ; 

 the aquatic Yapock (Chironectes), which feeds on fish and 

 smaller water animals. 



2. Family Dasyuridse. Carnivorous or insectivorous Marsupials. The 



limbs have clawed digits, five in front, four or five behind. The 

 canines are generally large. The stomach is simple ; there is 

 no caecum. 

 Examples. The Tasmanian wolf ( Thylacinus}, of dog-like form, 



dentition ^^, and the Dasyure (Dasyurus), civet-like, den- 

 3*34 



tition ^*, are specialised as carnivores. The members of the 



genus Phascogale are small and insectivorous. The banded 

 ant-eater (Myrmecobius) of W. and S. Australia, a somewhat 

 squirrel-like animal, has a long thread-like protrusible tongue, 



and more teeth than any other Marsupial, 4 * 3 ;j * ^. It differs 

 markedly from the other members of the family. 



3. Family Notoryctidse. This family has been erected for the mole- 



like Marsupial (Notoryctes typhlops), found in the sandy deserts 

 of S. Australia. It lives underground, is a rapid burrower, and 

 in its rudimentary eyes, keeled sternum, and some other respect* 



