440 Transactions. — Miscellaneous. 



marsupials, ^vhicll are characterized by the syndactyly of the 

 second and third toe, a pair of well-developed upper incisors, 

 accompanied by two pairs of smaller ones, and one pair of 

 strongly-developed lower incisors, and small or missing canines. 

 It now appears that in Patagonia deposits are existent whose 

 fossil mammals are entirely composed of Plagiaulacida. To 

 my knowledge, no Tertiary fauna of a similar composition is 

 known, but Marsh has lately described mammals from the 

 Cretaceous formation of North America which are lilcewise 

 exclusively composed of Plagiaulacida, and this is the reason 

 why I think it very probable that the Plagiaulacida of the river- 

 banks of the Eio St. Cruz, in Patagonia, belong to a Cretaceous 

 fauna. 



These Patagonian marsupials are not more nearly related 

 to any other group of living or fossil marsupials than to many 

 of the recent Australian genera. This is specially seen in the 

 simple quadritubercular structure of the teeth, whilst the 

 European and North American representatives show numerous 

 denticules, arranged in two or three rows, on their molar 

 teeth. This is found neither in Australia nor in Patagonia. 

 On this point I fully agree with Ameghino, but not that the 

 Plagiaulacida came from Patagonia into North America by 

 way of an Eocene migration, which'was geographically impos- 

 sible. Moi-eover, according to quite recent discoveries made 

 by Marsh, which were not then known to Ameghino, poly- 

 mastodont and quadritubercular Diprotodonta lived together 

 during the Cretaceous period in North America, and there can 

 be no doubt but that both types were already co-existent 

 during the Jura formation. But the genera with the serieswise 

 disposition of the mammiform tubercles in two or three longi- 

 tudinal rows do not seem to have reached the iVustralian 

 Archiplataic territory, or, at least, disappeared again at a very 

 early period. If, as Ameghino thinks, a land-communication 

 between North America and Argentina existed during the 

 Cretaceous epoch, this distribution would be inexplicable. The 

 genus Didelphys, which, however, occurs Tertiary in North 

 America, is also found in Europe ; and Didclphys, as the 

 descendant of its European precursors, the Peratheria, may 

 have sj)read to both Americas without having been compelled 

 to reach South America by way of North America. Didelphys, 

 which is wanting in Australia, must therefore be attributed to 

 immigration from the Old World. 



When x\meghino from this draws the conclusion that a 

 continent between Australia and Argentina must have been 

 in existence in the Mesozoic era, he only proclaims what Pro- 

 fessor Hutton, I myself, and many other scientists who have 

 studied the flora and fauna of both countries have done before, 

 but differing from Professor Hutton so far as to give this con- 



