rgos.] SINCLAIR— FAUNA OF SANTA CRUZ BEDS. 81 



to have become extinct with the Palaeothentinae at the close of the 

 Santa Cruz epoch, while the less specialized Caenolestinae were able 

 to persist to the present day. 



The Csenolestidae resemble the primitive phalangers in so many 

 respects that it is impossible to escape the conclusion that the two 

 families are related and not merely convergent groups. With the 

 exception of Halmarhiphus, a persistent ancestral type, the Santa 

 Cruz diprotodonts possess specializations in dental structure which 

 prevent their being regarded as direct ancestors of the phalangers, 

 but favor the idea that both groups are descended from a common 

 ancestry. 



Considerable evidence is now available to show that a land con- 

 nection between Patagonia and the Australian region existed noj 

 later than the close of the Cretaceous or beginning of the Tertiary * 

 and it is possible that at this time the interchange of marsupials 

 between the two continents was effected. Whether the marsupials 

 originated in South America and migrated thence to Australia, or 

 the reverse, can not at present be demonstrated, but a South Amer- 

 ican origin for at least some of the existing Australian and Tas- 

 manian types appears probable in view of their unmistakable rela- 

 tionships with Santa Cruz forms. 



Princeton University, April, 1905. 



EXPLANATION OF PLATES. 



Plate I. Cladosictis luslratus. Restoration based upon two specimens in the 

 collection of Princeton University. The skeleton measures 3 feet 

 over all. Restored parts are indicated by a cross. 



Plate II. Prothylacynus patagonicus. Restored from a single specimen in the 

 Princeton collection. The skeleton measures 4 feet 8^ inches 

 over all. The restored parts are indicated by a cross. 



1 For a summary of the evidence see Ortmann, Reports of the Princeton Uni- 

 versity Expeditions to Patagonia, Vol. IV, pp. 310-324. 



