724 MAMMALIA. 



B. DlPROTODONTIA. 



1. Family Epanorthidie. The selvas, a family of S. American forms, 



till recently believed to be entirely extinct. The existing forms 

 are included in the genus Ccsnolestes^ and two specimens only 

 have been found, but fossil remains are abundant. All are small, 

 and are remarkable in having the upper jaw of the polyprotodont 

 type, and the lower distinctly diprotodont ; and also in having all 

 the digits of the hind-foot free, whereas in all other living 

 Diprotodonts certain of these are united by skin (syndactylous). 

 They are probably primitive forms, and their presence in 

 S. America is highly important. There seems little doubt that 

 the Diprotodonts have been evolved in the Australian area from 

 a primitive widely-spread polyprotodont stock. If, therefore, the 

 Epanorthidie are really allied to the Diprotodonts, their exist- 

 ence in S. America seems to indicate a former connection 

 between that continent and Australia. 



2. Family Phascolomyidoe. - - The wombats, terrestrial, vegetarian, 



nocturnal Marsupials, somewhat bear-like in appearance. The 



dentition is rodent-like, - 1 '--, the teeth have persistent pulps, the 



incisors are chisel-edged, there being no enamel except in front. 

 In the embryo, however, there are four upper incisors, of which 

 the first persists, and five lower incisors, of which the third 

 persists. The fore-feet have five distinct toes, with strong nails ; 

 the hind-feet have a small nailless hallux, the second, third, and 

 fourth toes partly united by skin, the fifth distinct. The tail is 

 very short. The stomach is simple ; the aecum very short. 

 There is but one genus Phascolomys, with three species. 



3. Family Phalangerida.*. Small woolly arboreal nocturnal Mar- 



supials, with vegetarian or mixed diet. The fore-feet have five 

 distinct toes ; the hind-feet have a large, nailless, opposable 

 hallux, the second and third toes are narrow and bound together 

 by skin, the fourth and fifth free. The tail is generally long and 

 prehensile. The stomach is simple, the oecum usually large. 



Average dental formula, - j - 1 ' 2 ' 3 ' 3 ' 4 . 



1,0, 0-2, 3-4 



Examples. The grey Cuscus (Phalange)- orientalis] ; Tarsipes^ a 

 small mouse-like animal which feeds on honey, and is remark- 

 able in having no inflection of the angle of the mandible and 

 no oecum ; the flying phalangers (Pefmints], with a parachute 

 of skin extending from the little finger to the ankle ; the 

 Koala, or "native bear" (Phascolarctos cineirits), a relatively 

 large form, about 2 ft. in length. An extinct form, Thyla- 

 coleo, of the late Tertiary period of Australia, is interest- 

 ing in its extraordinary dentition, the functional teeth being 

 reduced to large front incisors and the third premolars, both 

 adapted for sharp cutting. 



