ORDER II MARSUPIALIA 31 



species about as large as rhinoceroses. Of Nototherium a nearly complete 

 skeleton has been found in Tasmania. Of Diprotodon several skeletons from 

 Lake Kallabonna, S. Australia, are known. All the phalanges of the first digit 

 of the hind-foot are fused into a single piece. Manus and pes practically 

 consist only of the enlarged carpals and tarsals and the fifth metapodium. 

 P and M are formed by two transverse ridges separated by a broad valley. 



Suborder C. POLYPROTODONTIA Owen. 



Carnivorous or insectivorous marsupials mostly of small or moderate size. 

 Dentition complete. In the upper jaw 4-5, seldom 3 ; in the lower jaw 3-4 

 small I. C pointed and high, frequently with two roots ; P with single cusps, 

 less frequently tvith secondary cusps, and mostly tvith double root; M in the 

 fossil forms often in greater number, in the recent forms four, triconodont and 

 tritubercular. 



To the polyprotodont marsupials belong the Australian Myrmecobiidae, 

 Peramslidae, Notoryctidae, JJasyuridae, the American Didelphyidae, and a large 

 number of fossil forms, among which the Pleistocene and Tertiary are closely 

 related to living genera, whereas the Mesozoic forms show peculiar, primitive 

 characteristics which make their classification in the zoological system difficult. 

 Owen considered the latter to be ancestors of the Polyprotodontia, and yet 

 emphasised their relationship to placental insectivores. 



Family 1. Dromatheriidae Osborn. 



(Protodonta Osborn ? Promammalia Haeckel.) 



P styliform with a single point. M with large central cone and smaller cusp 

 in front and behind, root imioerfectly divided. Lower jaw consists principally of 

 the dentary bone ; may have slight angular process. 



These small forms, represented by few imperfect remains, acquire special 

 significance, because they are thought to furnish a connecting link between 

 the Oynodontia and mammals. 



Dromatherium Emmons (Fig. 49). . 



Lower / upright, foremost P inclined forward, man- 

 dible without angular process. Microconodon Osborn. Fig. 49. 



With lower M and slight angular process, perhaps DromatUHum sylvestre Emmons. 

 . , ° . ^ . ^ , T , 1 Upper Triassic of Chatham, North 



With a separate angular bone in the mandible. Carolina. Lower jaw. i/j. 

 Upper Trias of North Carolina. 



Tribolodon Seeley. M with strong secondary cusps, but imperfectly 

 divided root, without angular process. Karoomys Broom, from the Trias of 

 South Africa, is imperfectly known. 



Family 2. Triconodontidae Osborn. 



Small marsupials with 4 P and 3-6 M. Pioots of the M absolutely divided. 

 P similar to M but simpler. M with three cusps arranged in a single row and 

 a conspicuous basal ridge or cingulum. C frequently with two roots. Angle 



