1910.] The Polyprotodontia. 203 



Metachirus, Didelphis. 

 Chironectes (Water Opossum). 

 Terrestrial-aquatic. 



Pes with webbed digits, inanus with external tubercle on carpus. 

 Tail flattened. 

 Piscivorous. 



Teeth as in Didelphis. 

 Dasyurid^ (derived from primitive Didelphiidae). 

 Chiefly terrestrial (primitively arboreal). 



Size increasing, from mouse-like (Phascologale) to badger-Uke 



(Sarcophilus) . 

 Tail non-prehensile, hairy. 

 Pes: hallux progressively reduced to zero. 

 Pes eleutherodactylous: digits parallel, II = III = IV. 

 Tarsus progressively elongating {Phascologale to Antechinomys) ; 

 or first elongating {Dasyurus), then broadening {Sarco- 

 ]>hilvs). 

 Tarsus with plantar pads fusing or modified. 

 Gait plantigrade-cursorial (Phascologale), to digitigrade-saltatorial 

 (Antechinomys) . 

 Insectivorous to carnivorovs. 



Polyprotodont: I ^^ median incisors becoming enlarged in insec- 

 tivorous forms; posterior premolar variable. 

 Molars varying from tritubercular with sharp piercing cusps in 

 insectivorous forms (Phascologale) , to sectorial in the carniv- 

 orous Sarcophilus. 

 Myrmecobiid^ (Derived from primitive Dasyuridse). 

 Terrestrial. 



Hallux reduced, slight traces of former syndactyly. 

 Insectivorous (ant-eating) . 



Polyprotodont. Dentition degenerating in adaptation to ant- 

 eating habits. 

 Molars irregvilarly cuspidate, of tritubercular derivation, number 



secondarily rising to ^ (Bensley). 

 Tongue elongate protrusile (Myrmecobius) . 

 Thylacynid^. Tasmanian Wolf and Tertiary " Sparassodonts " of Patagonia. 

 (Derived from veiy primitive unknown Dasyuridse). 

 Terrestrial. 



Size increasing, from opossum-like (Amphiproviverra) to coyote- 

 like (Borhycena) . 

 Hallux reduced or wanting. 

 Eleutherodactylous. 

 Semiplantigrade, cursorial. 

 Carnivorous, predaceons. 



Polyprotodont (I ^). 



Molars varying from tritubercular-sectorial to advanced sectorial 



type. 

 Amphiproviverra, Cladosictis, Prothylacinus, Thylacynus, Bor- 

 hycena. 



