1910.] The Diprotodonts. 215 



and to indicate a fair-sized incisor dentition. The lower jaw shows a deep 

 transverse groove on the alveolar border which may indicate the presence of 

 an enlarged grooved premolar or molar (Spencer, /. c, p. 784). A somewhat 

 similar deep alveolar groove occurs below the enlarged grooved p4 in the 

 Patagonian Csenolestoid Garzonia minima {cf. Ameghino, 1903, p. 157, 

 fig. 81). The glenoid region of the squamosal suggests the Diprotodont 

 type and the same is true of certain features of the femur, tibia and pelvis. 

 A closer comparison of Wynyardia with the Ctenolestoids seems desirable. 



IV. The Australian Diprotodonts. 



The probable course of adaptive and morphological divergence in the 

 dentition and foot-structure of the Diprotodontia have been very fully 

 worked out by Bensley (1903); his chief results may be summarized and 

 combined with the observations of others in the following table and in Fig. 

 14 (p. 202) : 



Adaptive Radiation of the Diprotodontia. 



H YPSIPRYMNOIDEA (Phalangeroidea) . 

 Phalangerid^. 



Phalangerin.e Bensley. (True Phalangers.) 

 Arboreal. 



Size, from mouse-like (Dromicia) to opossum-like (Trichosurus). 

 Tail prehensile, partly scaly (Dromicia), to bushy (Trichosurus). 

 Pes: hallux fully opposable. 

 Syndactyly in pes marked, digit IV large to very large (Dactylo- 



psila) . 

 Tarsus with plantar pads primitively separate and transversely 



striate (Acrobates). 

 Gait plantigrade, climbing; Acrobates and Petaurus with flying 

 membranes. 

 Insectivorous to omnivorous, to vegetarian. 

 Diprotodont, I. y, C. ^. 

 Molars quadrituberculate, cusfDs bunoid, no external styles or 



intermediate conules. 

 Acrobates, Distoeckurus, Dromicia, Gymnobelideus, Petaurus, Dac- 

 tylopsila, Phalanger, T7-ichosurus. 

 Tarsipedin^ Bensley. 

 Arboreal. 



Size small. 

 Tail prehensile. 



Pes rather long, with opposable hallux, hallux nailless. 

 Syndactyly in pes extreme, D. IV greatly enlarged. 

 Mellivorons-insectivoroiis. 

 Diprotodont. 



