MIGRATION OF TERRESTRIAL VERTEBRATES 301 



between the two countries. The first proof is 

 supplied by the presence of some common genera. 

 The terrible Megalosaurus, which inhabited Europe 

 from the Bathonian to the Cretacean, is found again 

 in the upper Jurassic of Colorado, and the same type 

 continues, with hardly any change, as the modified 

 Lcelaps of the upper Chalk of New Jersey and of 

 Montana ; and the migration of this European genus 

 into America does not appear doubtful. In the 

 family of Cseluridse, with longer and slender paws, 

 the genus Tanystrophceus is found identical in the 

 Muschelkalk of Bayreuth and in the Trias of New 

 Mexico. Finally, among the ponderous Stegosauridce, 

 with their powerful dermic armour, the genus Stego- 

 saurus is the same, according to Marsh, as the 

 Omosaurus of the Kimmeridgian of England. 



A second order of proofs, rather less direct, results 

 from the passage from one country to another, 

 not of genera, but of highly specialized families or 

 groups of terrestrial animals. Such is the case with 

 the voracious Turtle- Alligators, or Chelydridce, and 

 ihePleuroderous Turtles who passed from Europe into 

 America in the upper Cretacean period, and are still 

 in existence, the first in the rivers of North America, 

 the latter in the fresh waters of the Southern 

 Hemisphere. The entire order of Dinosaurian 

 Sauropods made its appearance in Europe as early 

 as the Bathonian, and may well have passed into 

 America only in the upper Jurassic. Lastly, there 

 is no doubt that the entire group of flying Reptiles 

 or Pterosaurians, appearing early in the Rhsetian 

 of Suabia, emigrated to America and are found in 

 the upper Jurassic of Colorado. 



