112 THE NEOG^IC REALM. [CHAP. 



themselves. Assuming their affinities with the Australian type 

 to be rightly determined, they constitute a most important link 

 in the chain connecting the faunas of South America and Aus- 

 tralia. 



In the last chapter it has been argued that, from the absence 

 of allied forms in the Tertiaries of North America and Europe, as 

 well as from their resemblance to the Australian dasyurids, it is 

 difficult to come to any conclusion other than that the ancestors of 

 the Santa Crucian polyprotodont marsupials reached the country 

 from Australia, either by way of the Antarctic continent, or by a 

 land-bridge in a more northern part of the Pacific. If this be 

 correct, and likewise the supposition that the opossums origi- 

 nated from the ancestral stock in South-eastern Asia, it will be 

 evident that Didelphys and Ccenolestes met in South America 

 after their ancestors had travelled half round the world in opposite 

 hemispheres. 



It may be added that the alleged occurrence of monotremes 

 in the Santa Cruz beds is due to bones of aberrant armadillos 

 (Peltephilus) having been mistaken for those of that group 1 . 



Although in this volume the writer avoids laying much stress 

 upon aquatic mammals, it may be mentioned that 



Cetaceans. 



there are two genera ot dolphins belonging to the 

 family Platanistidce, each represented by a single species, which are 

 peculiar to the Neogaeic realm. These are Stenodelphis (Pontoporia] 

 from the mouth of the Rio de la Plata, and Inia of the upper 

 Amazon; the only other existing representative of the family 

 being Platanista of the larger Indian rivers. 



After the foregoing survey of the chief features of the recent 



and fossil mammalian fauna of the Neogaeic realm, 

 tinction ofThe ^ ts g enera l bearings on the relations of South America 



t o other parts of the world may be taken into con- 



sideration. It will, however, facilitate matters to 

 give a tabular view of the orders, suborders, and families of non- 

 volant land mammals represented in the realm. In the following 

 table such groups as are either confined to Neogsea, or have only 

 reached North America at a comparatively recent epoch are 



1 See Lydekker, An. Mus. La Plata Pal. Argent. Pt. III. p. 67 (1894). 



