or THE AUSTEALIAN MAESUPIALIA, 



193 



DASYURIDiE. 



Beginning witli the hypothetical stem-form, to Avhich we assign the characters of the 

 Dideliihyidtc, we first note the fact that the radiation has proceeded along two primary 

 lines. One of these, distinguished hy its insectivorous-carnivorous dental evolution, 

 and by its arboreal-terrestrial foot-evolution, in which the primitive eleutherodactylous 

 condition of the digits has been retained throughout, leads to and culminates in the 

 present family. 



Tluilciwius. 



Sarcophihts. 



Dasijurus, 

 terr. spec. 



Dasyuroides. 



Chcetocercus. 



basyurus, 

 arb. spec. 



Antechinomys. 



\ 

 N . 



Sminthopsis. 



Plmscogale. 



Myrmecobius. 



As shown by the dentition, the stem-form for the Dasyurida? must have been a small 

 species of Phascoyale. Considering size, dentition, and foot-structure together it is 

 probable that P. Jlavipes makes the closest approach to this prototypal form. The 

 dental evolution of the predominant section of the family, or Dasyurinne, has been 

 referred to as homogeneous and progressive throughout, but the general sequence is 

 disturbed by the occurrence of successive lines of terrestrial modification in foot- 

 structure. We are thus obliged to recognize a main insectivorous-carnivorous arboreal 

 line extending through the species of Plmscogale and ending in Dasyiirus. Sminthopsis, 

 which has been referred to as, on the whole, more primitive than Phascogale in dentition, 

 this remark referring chiefly to the less reduced or wholly unreduced character of the 

 posterior premolars, in reality represents a terrestrial derivative of that genus, the 

 various species, beginning with ^S*. leucopus, showing successive stages in the development 

 of a digitigrade type of pes. The small size of the species of Sminthopsis and their 

 primitive dental characters, together with the transitional type of pes presented by 

 S. leucojms, distinguish them from the larger terrestrial forms, and establish the fact of 



