444 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



dentia. The characters which they possess are in no respect transitional 

 to the Multituberculata. The Paucituberculata, like the Sparassodonta, 

 are a group founded on a misconception of relationships and should be 

 abandoned. 



BEARING OF THE SANTA CRUZ MARSUPIALS ON 



ZOOGEOGRAPHY. 



The reality of a former land connection between the Australian region 

 and South America is plainly indicated by several lines of evidence based 

 on the distribution of fishes, land shells, decapod crustaceans, plants, and 

 Tertiary marine molluscs (Ortmann, 1902). This land connection is be- 

 lieved to have existed not later than the close of the Cretaceous or be- 

 ginning of the Tertiary, and it is only by such a connection that the 

 distribution of the Thylacynidae can be explained. The direction, 

 continuity or discontinuity of this land bridge need not enter into the 

 present discussion. So far as the Thylacynidae are concerned, there can 

 be little doubt of their South American origin, judging from the marked 

 adaptive radiation which they attained during the Santa Cruz epoch, but 

 whether the same can be said of marsupials in general is still a matter of 

 question. It is believed, however, that the order may be properly regarded 

 as of southern origin and that the occurrence of opossums in North 

 America and Europe may be explained as the result of migration from 

 the southern hemisphere. 



MARSUPIALIA INCERT^ SEDIS. 



A large number of Santa Cruz marsupials have been named by Ame- 

 ghino and Mercerat, which are not represented in the collections at 

 Princeton University and the American Museum of Natural History. 

 Many of these have never been figured and are very imperfectly known. 

 At present, the writer is not prepared to add to what has been published 

 regarding them. The names and full references to the literature are here 

 given. 



BORHY^NA Ameghino. 



BORHYENA FERA Ameghino. 



Dynamictis fera Amegh. ; Revista Argentina, pp. 148-149, fig. 53, 1891. 

 Dinamyctis fera (sic] Amegh.; Ibid., p. 314. 



