1910.] " Diadactyla and Syndactyla." 217 



DiPROTODONTID.E. 



Terrestrial. 



Size very large, about that of a small Megatherium, but with 



enormous head. 

 Pes with very large tarsus and reduced digits, turning inward, 



the outer elements much enlarged (Stirling and Zietz). 

 Digits II and III subequal and showing traces of syndactyly. 

 Herbivorous. 



Diprotodont, with enlarged procumbent I y; i-, i^ small. 

 Molars completely bilophodont. 

 "fNototherium, ^Diprotodon. 

 Thylacoleontid.e. 

 Terrestrial ? 



Size that of a small lion. 

 Carnivorous ? (Broom, 1898). 



Diprotodont, with enlarged compressed, piercing-cutting median 



incisors. 

 P|, greatly enlarged, shearing; molars much reduced, tubercular. 

 t Thylacoleo. 



V. Summary of the Arguments in Favor of Retaining the Divisions 



"Polyprotodontia" and "Diprotodontia" rather than 



"Diadactyla" and "Syndactyla." 



(1) The nearer affinities of the .syndactylous Peramelidre are apparently 

 with the Polyprotodontia rather than with the Diprotodontia. 



(2) The Cienolestidff', perhaps more nearly allied to the Diprotodontia, 

 are non-syndactylous (p. 211). 



(3) One species of the Polyprotodont Marmosa, the most primitive 

 living genus of Marsupials, shows a marked tendency toward syndactyly 

 (Bensley, 1903, pi. vii, Fig. 7). 



(4) " Poli/protodontia" and "Diprotodontia" may be defined from 

 several characters but "Diadactyla" and "Syndactyla" from but one char- 

 acter. 



VI. Primitive Mammalian Characters of the Marsupial Skull. 



Com pari .son of the skulls of Marmosa and Didelphis. 



Additional reasons for believing that the smaller Didelphidae are 

 structurally prototypal to the remaining Marsupials are found in the general 



t Extinct. 



