ON THE ZOOLOGICAL POSITION OF TEXAS. 



By E. D. Cope. 



The relation of the nearctic and neotropical faunae at their point of 

 junction is as yet a problem not fully solved. Where there is placed 

 between the two an obstacle to migration of land and fresh water ani- 

 mals, as between the Gulf coast of the United States and the islands of 

 the West Indies, the differential characters of the faunte are well marked ; 

 but where the northern continent gradually i^asses into the long isth- 

 mus of Mexico, the case is far different. Here no barrier obstructs the 

 passage of animals from the one region to the other, and nothing but 

 climatic and meteoric causes can limit the range of the types of either 

 fauna. A careful investigation of this subject must have an important 

 bearing on the whole subject of the influence of environment on animal 

 life. 



In general the studies into the zoology of Mexico have shown conclu- 

 sively that the high plateau is populated by an animal life which differs 

 from that of the coastward plains, or Tierra Caliente. The highest land 

 is known as the Tierra Alpina, and the intermediate region is the Tierra 

 Templada. As residents of the land incapable of performing migrations, 

 the Batracliia and Rcptilia oft'er the most excellent field for the deter- 

 mination of the boundaries of these districts. 



From this source we learn that the line of demarkatiou between the 

 great Northern and Southern realms is the very sinuous and irregular 

 one which separates the Tierra Caliente from the Tierra Alpina. The 

 genera of South America advance northwards along the lower lands of 

 Central America and Mexico, terminating their range at various points, 

 but enough of them remain at Matamoras, at the mouth of Eio Grande, 

 to show that that point is not far from the northern boundary of the 

 neotropical realm. On the other hand, various genera of the southern 

 regions of North America extend their range southward as far as the 

 city of Mexico. This southern extension is not homogeneous in its 

 character, since two very distinct groups of reptilian life are represented 

 on each side of the political boundaries of the two countries. In North 



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