46 



ON THE ZOOLOGICAL POSITION OF TEXAS. 



The summary of the above lists of the species of the Plateau district 

 is as follows: Found in the Sonoran region, nineteen species; peculiar, 

 eleven; found in the warm parts of Mexico, five; found in the Central 

 region, seven. The Mexican list is reduced hy the fact that one of its 

 species is also Sonoran ; and the Central list by the exclusion of four 

 species, which are also Sonoran. 



It is now evident that the characteristics of the fauna of the Plateau 

 region of Texas refer it to the Sonora region, of the ISTearctic realm, un- 

 less the number of its peculiar species is so large as to necessitate the 

 recognition of another primary division. This course is negatived, not 

 only by the fact already shown, that there is no genus lieculiar to this 

 district, but by the character of the list of species enumerated as peculiar 

 to it. Of the eleven species of this list, six are rare in collections, and 

 it is quite uncertain what the extent of their range in the district really is ; 

 but should the entire number (eleven) prove to be limited to the Plateau 

 district it would only entitle it to be regarded as a subdi\ision of the 

 great Sonoran region. The addition of Cynomys ludovicianus, Bos ameri- 

 canus, and Cho7'opMlus triseriatus from the Central fauna, which do not 

 occur in the typical Sonoran list, adds some weight to' this conclusion. 

 We have now attained to what has heretofore been a desideratum, the 

 eastern limit or boundary of the Sonoran region. This, it appears, is the 

 eastern and southern border of the Plateau district, which extends 

 southwards to within twenty miles of San Antonio, and runs northeast- 

 ward, crossing the Colorado Eiver not far northwest of Austin, and then 

 passes northwards, crossing the Brazos near Weatherford. 



