POLYPROTODONTIA. 530 



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-like, tongue long, extensile ; lower lip pointed ; back 

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

 usual number of 7 ; dentition i 4 c \ p i m , ''' . , without pouch, 

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

 S. Australia, 1 species. 



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

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

 upper molars tritubercular, pouch opening backwards, central South 

 Australia, one genus and species. Notoryctes Stirling. 



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

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

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

 simple ; caecum small or moderate ; dentition i^Cxpfw^; pouch 

 generallj^ absent, sometimes represented by two folds of skin, N. and S. 

 America, fossil in Eocene, Oligocene and Miocene of Eiu-ope 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 number of 

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

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

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

 Filhol., from the Oligocene and Miocene of Em-ope and Peratherium 

 from the Eocene and jNIiocene of Eiu-ope and America, and from the 

 Pliocene and Pleistocene of America, belong to tliis family. 



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

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

 tions with the polj^rotodont marsupials. These include the celebrated 

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

 of the Middle Purbeck Beds (U. Jurassic) of Dorsetshire. Apparently 

 similar remains are found in N. America in the U. Jm-assic and U. Creta- 

 ceous formations, and two forms, \'iz. Dromatherium and Micronodon 

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

 for associating these remains, which belonged to ciuite 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 shghtly inflected. The den- 

 tition resembles that of Myrm,ecobius, and consists of at least three lower 

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



These forms have been grouped in families which are here tabulated 

 as an appendix to the Polypi-otodontia, for convenience of reference and 

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



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

 with main cusp and several anterior and posterior smaller accessory 

 cusps all in the same line ; dentition of mandible * 3 c 1 p 3 m 7 ; 

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

 cnnodon Osborn, Dromatherium Emmons. 



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



* Stirling, Trans. Boy. Sac. S. Australia, 1891, p. 154 ; Gadow, P.Z.S., 

 189-2, p. 361. 



