MAY, 1921. AMERICAN MARSUPIAL, C-ENOLESTES OSGOOD. 151 



premolariform canines, specialized posterior premolar; (g) in the 

 urinogenital system presence of round ligament, median vaginae 

 indicating parturition by direct median passage; (h) in the 

 alimentary canal small caecum. 



3. It has few non-marsupial characters and no great degree of 

 specialization. 



The important characters not shared with at least some other 

 marsupials are: (a) the preorbital vacuity found elsewhere only 

 among ungulates; (b) the large persistent mastoid foramen; (c) 

 the large carotid canal; (d) the very short pubic symphysis; 



(e) the extended articular surface of the trochlea of the humerus; 



(f) the sesamoid in the supinator tendon. 



The cardiac gland of the stomach has a counterpart in Phas- 

 colarctos and Phascolomys; otherwise it is unique among mar- 

 supials. 



4. It has no especial affinity to the American Didelphiidae. 

 Except for a few relatively unimportant myological char- 

 acters concerning which data are not available for many Australian 

 forms, Ccenolestes shows practically no exclusive resemblances to 

 the didelphids. On the other hand it differs from them in numer- 

 ous characters including nearly all the above-mentioned resem- 

 blances to the Peramelidae. 



5. The ancestor of the canolestids was probably a northern form 

 which had already separated from the generalized polyprotodont 

 stock. 



This conclusion is based chiefly upon the probable affinity of 

 C&nolestes to modern peramelids and of both to the Eocene 

 Myrmecoboides which partially fulfils the hypothetical require- 

 ments of the ancestral diprotodont. Many considerations favor 

 this assumption. 



6. The North American ancestor of the canolestids possibly extended 

 throughout Holarctica and therefore may also have given rise to 

 the Australian diprotodonts. 



This assumes that the main lines of divergence between dipro- 

 todonts and polyprotodonts were established in the north prior to 

 the Australian and South American radiations. Hence an Antarc- 

 tic land connection is not necessary to explain the resemblances 

 between American and Australian marsupials. 



7. The phylogenetic and morphological relations of C&nolestes are 

 best expressed by classifying it in the suborder Diprotodontia, 

 family Pal&othentidae, subfamily C&nolestinae. 



