136 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. XIV. 



formula, molariform teeth with hypocone, lower incisors proclivous, 

 lateral upper incisors compressed, reduced canines and premolars, 

 specialized posterior premolar, movable cervical rib, osseous patella, 

 large median vagina, cursorial structure of legs, first and fifth toes of 

 forefeet reduced, caecum small, tail not prehensile. Many of these 

 characters, while not diagnostic of the diprotodonts as a group are 

 present in the majority of that group and absent in the majority of 

 polyprotodonts. 



It may be concluded, therefore, that diprotodonty in the ceenolestids 

 may have originated in one of three ways: 



(1) from didelphid pre Miocene types through undiscovered inter- 

 mediate forms existing prior to the differentiation of the peramelids. 



(2) from an ancient line now represented by Myrmecobius. 



(3) from primitive peramelids after their separation from the 

 dasyurid-didelphid stem. 



The first of these is the theory of Bensley and in general of those 

 who have followed him. The second is perhaps less entitled to con- 

 sideration, but is still not wholly baseless. The third is to the writer 

 more probable than either of the others. 



RELATIONSHIPS OF WYNYARDIA. 



The extinct mareupials known from the Australian region are nearly 

 all of Pleistocene age and unequivocably diprotodont or polyprotodont. 

 The most conspicuous exception to this is Wynyardia bassiana Spencer 

 (1900) from beds at Table Cape, Tasmania, which are regarded as late 

 Eocene or early Oligocene. This form, the remains of which include 

 parts of limb bones and an imperfect skull without teeth, exhibits such a 

 curious mixture of characters that it has so far been omitted from formal 

 classifications. Spencer summarizes his study of it as follows: "A 

 consideration of all the features would appear to lead to the conclusion 

 that the fossil is the representative of a now extinct series of forms which 

 were more nearly allied to ancestral Polyprotodonts than are any of the 

 existing Diprotodont forms. It may, in fact, be regarded as inter- 

 mediate between the former and the latter, and as indicative of a stage 

 in the development of Australian marsupials when the ancestors of the 

 recent diprotodontia were beginning to diverge from the original 

 Polyprotodontid stock from which they have been developed within the 

 limits of the Australian region." 



Bensley (1904, p. 200) is somewhat more definite, saying: "While it 

 would be difficult to add to the excellent comparisons presented by 

 Spencer, it is probable that the reference to the animal as an inter- 



