mi.] AND ANCIENT GEOGRAPHY. 38/ 



II. JVew World (America). This is North America and Sclater's 

 Neogcea. I think there is no objection to use Neog^a for the 

 whole of the '' New World." 



III. Australia. This is Sclater's Noiog^a. 



IV. Madagascar. Although of small size, the historical 

 development warrants a consideration of Madagascar as a separate 

 centre. In fact, it is — aside from Australia — the oldest isolated 

 part of the world. 



V. Antarctica. This is no longer a centre of radiation ; it is 

 now barren of continental life. 



Note — We claim that this division solves the problem ofzoogeographi- 

 cal research as indicated by Osborn, and amended in the introduc- 

 tion (seep. 269, footnote 3) : it unites historically and geitetically past 

 and present conditions of distribution of continental life — that is to 

 say, it gives a division that is founded upon the present physical 

 features of the earth's surface as related to life, and pays due atten- 

 tion to the past history of the earth. But this division takes into 

 consideration only the chief topographical chdiXdiCitr?, ; yet there are 

 others, especially those connected with climatic differentiation, 

 which are apt to furnish additional points of view in dividing the 

 earth in zoogeographical units. By using the latter we shall arrive, 

 with only slight changes,^ at Wallace's regions^ which, as we have 

 mentioned above (p. 271), are well supported hy physical characters y 

 although Wallace constructed them according to entirely different 

 principles. 



B. History of the Distribution of Crayfishes. 

 (Compare Fig. i, p. 275.) 



1. In the Lower Cretaceous we are to assume that the ancestors 

 of the Potai7iobiidce and Parastacidce lived in Si no- Australia, possi- 

 bly extending to its southern extremity, Antarctica. 



2. During the Middle Cretaceous, Astacoides reached Madagascar 

 by way of the Lemurian land-bridge, coming from the Sinic conti- 

 nent. Shortly after this, in the Upper Cretaceous, the separation 

 of eastern Asia and Australia took place, resulting in the differen- 

 tiation of the families Potatnobiidoe (in the Sinic continent) and 

 Parastacidce (in Archinotis). At the same time, the Pota7nobiida: 

 extended their range into western North America, going as far as 

 Central America. Thus, in the Upper Cretaceous, the PotamobiidcE 



^ This refers to Madagascar. 



