PALEOGEOGRAPHY OF ANTAECTICA HEDLEY. 445 



he supposed to liave traveled down the Andean Chain and crossed to 

 Australasia by the Antarctic route. 



Summing up a biological examination of the southern islands of 

 New Zealand, Prof. C. Chilton concludes: "The evidence pointing to 

 former extensions of land from the Antarctic Continent northward, 

 and to the warm climate that was enjoj^ed by this continent in early 

 Tertiarv^ times, seems to offer a fairly satisfactory explanation of the 

 facts before us." (Subantarctic Islands of New Zealand, vol. 2, 

 1909, p. 467.) A full bibhography is included in this article. 



Fmally, Osborn describes the hypothetical reconstruction of Ant- 

 arctica as "one of the greatest triumphs of recent biological investi- 

 gation." C'The Age of Mammals," 1910, p. 75.)^ 



2. ARGUMENT. 



The distribution records of recent and fossil species upon which 

 the generalizations of the foregoing authors depend have never been 

 denied. Indeed, they continue to increase with the progress of 

 science. 



To other, and usually earlier, authors these views presented two 

 insuperable difficulties. One is the extreme change in climate which 

 formerly permitted temperate and subtropical animals and plants to 

 exist where cold is now so intense. The other is the demand for the 

 existence of Tertiary land where an ocean now extends so broad and 

 deep as that between Antarctica and Tasmania or New Zealand. 



To evade these difficulties and yet explain existing distribution the 

 followinsr three alternatives have been advanced : 



That decadent groups were expelled from their original seats by 

 more vigorous competitors; retreating from a northern center to the 

 ends of the earth, such groups divided into fugitive parties which con- 

 verged as southern lands apj)roached the pole. Or discontinuous 

 distribution in southern continents were simply considered remnants 

 of a former universal distribution. (Wallace, "The Geographical 

 Distribution of Animals," vol. 1, 1876, p. 398; PfefTer, Zool. Jahrb. 

 Suppl. vol. 8, 1905, pp. 407-442.) 



But whereas, under the circumstances postulated, the northern wan- 

 derers would be expected to diminish and to vary as they receded, the 



1 While this article was in the press there reached me an important memoir by T)r. Pilsory on "The 

 Non-Marine MoUusca of Patagonia.'' (Uep. Princeton Univ. Exped. Patagonia, in, 1912, pt. v, pp. 513- 

 633.) My friend considers Antarctica rather as a road for migration, especially an American exit, than as a 

 center of evolution. He takes exception to my derivation of Australian Acavida^ from Antarctica and 

 suggests that the group arose in Gondwana Land. On reconsideration I would still maintain that the south- 

 eastwardly Increasing distril)ution of Australian Acavida; indicates their immediate Antarctic origin. 

 But previous to an Antarctic sojourn the group may have been Gondwana bred. This memoir heightens 

 the resemblance between ea.st and west. Gundlachia, Diplodon,and Radiodiscus are cormaon, PetterdiaTia 

 scarcely diflers from Littoridina, and I'otamolUhis appears to have Tasmaniau relatives. 



