MIGRATION OF TERRESTRIAL VERTEBRATES 299 



Angara precludes the study of possible migrations 

 between these two northern masses. 



But so far as the Western mass is concerned, we 

 know that subsidences occurring in the North 

 Atlantic early brought about a separation, for at 

 least a time, between the lands risen from the 

 sea in Northern Europe and those in Northern 

 America, comprising therein Canada and a good 

 part of the United States. Yet this separation 

 did not exist at the Permian epoch, as is testified 

 by several types of Amphibians and even of terres- 

 trial Reptiles, such as the Naosaurus, common to 

 the two regions. 



It would seem that communications may still 

 have continued to exist, though with greater diffi- 

 culties, up to the end of the Trias, as is indicated 

 by the presence in Connecticut of Crocodiles of the 

 Beloder genus, and of the Dinosaurians, Palceo- 

 saurus and Thecodontosaurus. But from the Lias 

 onwards a great number of families and even of 

 orders of terrestrial Reptiles become peculiar either 

 to Europe or to America. Among the long-beaked 

 crocodilians, the Teleosauridce and the Metriorynchidce 

 are exclusively European families. Among the 

 Dinosaurians of exclusively terrestrial habitat, the 

 Scelidosauridce, great herbivorous animals with 

 spatuliform teeth, dwelt on the European Conti- 

 nent from the Lias to the lower Cretacean. It is 

 the same with the gigantic Iguanodons, with their 

 tripod gait, recalling the existing kangaroos. On 

 the other hand, the great horned flesh-eating 

 saurians or Ceratosauridce are confined to the upper 

 Jurassic of the United States. 



