ON THE ZOOLOGICAL POSITION OF TEXAS. 43 



divisions, as they liave not an extensive range. Those fonnd in Texas 

 are marked with an asterisk : 



Ghilomeniscus ; Gyalo])iuni; Hypsujlena ; Phimothyra;* Helodetma; 

 CalUsanrus ; Saurojiialus; Ufa.* 



The middle column of the three above given may be redivided into 

 those which belong to the Mexican district alone, and those which are 

 fonnd both there and in one or more of the South American districts. 

 But this discussion belongs rather to that of the relations of the Mexican 

 fauna. 



The consideration of the vertebrate fauna of Texas will be now chiefly 

 limited to the Mammalia, Beptilia, and BafracMa, as the forms which 

 are most fixed in theu* range and most intimately related to the physical 

 history of the surface of the earth. The distribution of the areas of 

 elevation and of the drainage have been already i)oiuted out in the 

 opening of the article. It was shown that the surface of Texas rises to 

 the northwest, and that the strikes of the strata, as well as of the faults 

 of the formations, have a northeast and southwest direction. It has 

 been pointed out that the climate west of the 9Sth meridian is character- 

 ized by aridity, while the eastern i)ortion of the State is supplied with 

 abundant rains. The annual amount of rainfall on the eastern border 

 of the State is, according to Blodgett,t fifty inches. At the meridian 

 of the western or Mexican coast of the Gulf (he amount is reduced to 

 thirty-five inches. From this point westward the amount diminishes 

 rapidly. Thus, in longitude 98^ 30', about the border of the first plateau, 

 tbe rainfall is twenty- five inches; at Fort Concho it is reduced to 

 twenty inches, and on the high plains of the Pecos to but fifteen inches. 

 Of coiu'se change of vegetation accompanies this climatic gradation, 

 and animal life is modified in proportion as it is dependent on plants. 

 Such change affects many birds and arboreal mammals, reptiles, and 

 BatracMa. Of tree-livers may be especially mentioned the Scclo]}ori, 

 spinosus and consobrimis, and the Sylce. 



"We may now place in connection with the facts of geology and clima- 

 tology the distribution of the Vertehrata considered in the previous 

 pages. The species will be taken up in geographical groups. These, 

 which have been already foreshadowed, are four in number. First, 

 those of the extreme southwest; second, those of the plateaus; and 

 third, those of the low country and the east. These will be i)laced in 

 three columns, so that the common and peculiar si^ecies may be com- 



t Climatology of tlie United States ; also, Gray's Atlas, p. 26. 



