688 MAMMALIA. 



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 specialised 

 than the Polyprotodonts, and are more modern. They have a caecum. 



S- 



A. POLYPROTODONTIA. 



I. 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 caecum 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 

 4 I 34* 

 Examples. — The Virginian or crab-eating opossum (Didelphys 

 marsupialis), with a pouch ; the woolly opossum (Z>. lanigera) ; 

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

 smaller water animals. 

 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 ( Thylacinm), of dog-like form, 



dentition i-=^, and the Dasyure [Dasyurus), civet-like, den- 

 tition - — -, are specialised as carnivores. The members of the 



3124' r 



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 ii 3 ^-?!--. It differs 



3135 or 6 



markedly from the other members of the family. 



Family Notoryctidse. — This family has been erected for the 

 recently-discovered 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 respects, markedly resembles the Eutherian mole. 

 It is thus a good illustration of "convergence," i.e. the appear- 

 ance of similar characters in forms not nearly related, apparently 

 in indirect response to similar conditions of life. 



Family Peramelidse. — The burrowing bandicoots, all small in size, 

 insectivorous or omnivorous in diet. In the fore-feet two or 

 three of the middle toes are well developed and clawed, the 

 others being rudimentary ; in the hind-feet the hallux is small or 

 absent, the second and third toes are very slender and united 

 in the same fold of skin, the fourth toe is very large, the fifth 



