ON THE ZOOLOGICAL POSITION OF TEXAS. 



45 



peculiar to this section, so far as known, but its boundaries on the south- 

 west have not been ascertained. 



If now we examine column three, which, though incomplete, gives a 

 general idea of the species of the eastern part of the State, we have a 

 list of the well-known species of the Austroriparian region, with per- 

 haps the single exception of the Trojnclonotus clarM, whose eastern 

 range is unknown. We derive from this, that Texas, southeast of the 

 first plateau, must be included in that primary region. 



Forty species are enumerated as characteristic of the plateau districtj 

 and they present afl&nities in three directions. These are to the Mexi- 

 can fauna of the Tierra Caliente, to the Sonoran fauna of Mexico and 

 the United States, and to the fauna of the central region or that of the 

 great plains of North America. Some of the species are peculiar to the 

 plateaus, and others are found in all the regions named. I first indi- 

 cate the relationships of the genera, omitting those which are uni- 

 versally Nearctic. 



From the preceding tables it is evident that the Plateau district owes 

 the character of its fauna chiefly to the predominance of Sonoran genera. 

 There are ten of these, four of which are also Mexican and two Central. 

 There are two Mexican genera of frogs, but it is very uncertain whether 

 they are "widely distributed in the Plateau region. A most important dif- 

 erence between this and the Austrorii^arian region is at once ai)parent. 

 No genus is iJeculiar to the Plateau district of Texas. 



In considering the corresponding relations of the species, I add to 

 the three already defined, a fourth list, which consists of those peculiar 

 to the Plateau district in Texas, so far as yet imperfectly known. 



