POLYPROTODONTIA. 539 



Papuan and Australian regions, 13 species. Sminthopsis Thomas, small 

 forms with hallux and pouch, Australia and Tasmania, 4 species. Ante- 

 chinomys Krefft, jerboa-like, terrestrial, without hallux, Queensland and 

 N. S. Wales. Myrmecobius Waterh., arboreal and terrestrial, anteaters, 

 red and squirrel-Uke, tongue long, extensile ; lower hp pointed ; back 

 banded with white, hallux absent, molars and premolars exceeding the 

 usual number of 7 ; dentition i ^ c i p ^ m ^^, without pouch, 

 alHed by its dentition to the Jurassic polyprotodont marsupials, W. and 

 S. Australia, 1 species. 



Fam. 3. Notoryctidae,* mole-marsupial, red colour, mole-Uke form 

 and habits, without externally visible eyes or ears, pentadactyle hmbs, 

 upper molars tritubercular, pouch opening backwards, central South 

 Australia, one genus and species. Notoryctes Stirling. 



Fam. 4. Didelphyidae. Opossums, arboreal (except Chironectes mini- 

 mus which is aquatic), carnivorous or insectivorous, pentadactyle forms 

 with an opposable hallux for climbing. Tail long, prehensile ; stomach 

 simple ; ca«cum small or moderate ; dentition tfcipfmf; pouch 

 generally absent, sometimes represented by two folds of sldn, N. and S. 

 America, fossil in Eocene, OUgocene and Miocene of Europe and America ; 

 two genera. Didelphys L., hind toes free, size from that of a cat to a large 

 mouse, with 23 species (this genus has been divided into a niunber of 

 sub-genera, Didelphys, Metachirus, Philander, Micoiireus, Peramys). 

 Chironectes 111., water opossum, hind toes webbed to their extremities, 

 about the size of a rat, Guatalema to S. Brazil, 1 species. Amphiperatherium 

 Filhol., from the OUgocene and IMiocene of Europe and Peratherium 

 from the Eocene and Miocene of Europe and America, and from the 

 PUocene and Pleistocene of America, belong to this family. 



A number of fossil forms known by httle more than their lower jaws 

 and teeth and foimd in Mesozoic rocks, are associated in current classifica- 

 tions with tlie polyprotodont marsupials. These include the celebrated 

 lower jaws of the Stonesfield Slate (Lower Jurassic) of Oxfordshire and 

 of the ]\Iiddle Purbeck Beds (U. Jurassic) of Dorsetshire. Apparently 

 similar remains are found in N. America in the XJ. Jurassic and U. Creta- 

 ceous formations, and two forms, viz. Dromatherium and Micronodon 

 are known by lower jaws in the Upper Trias of CaroUna. The reasons 

 for associating these remains, which belonged to quite small animals no 

 larger than a rat, with the marsupials are indeed slender, based as they 

 are only upon the dentition of the lower jaw and upon the fact that in 

 some of them the angle of the mandible is slightly inflected. The den- 

 tition resembles that of Myrmecobius, and consists of at least three lower 

 incisors, well-developed canines and cuspidate molars and premolars. 



These forms have been grouped in famihes which are here tabulated 

 as an appendix to the Polyprotodontia, for convenience of reference and 

 not because any real importance can be attached to the grouping. 



Fam. 5. Dromatheriidae. Premolars styUform, molars triconodont, 

 with main cusp and several anterior and posterior smaller accessory 

 cusps all in the same line ; dentition of mandible i S c I p S m 1 ; 

 from the U. Trias of CaroUna ; by many regarded as reptiles. Micro- 

 conodon Osborn, Dromatherium Emmons. 



Fam. 6. Triconodontidae. With 4 premolars and 4—8 molars ; canines 



* Stirhng, Trans. Roy, Soe, S. Australia, 1891, p. 154 ; Gadow, P.Z.S., 

 1892, p. 361. 



