UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



ZOOLOGY 



Vol. 12, No. 14, pp. 399-410 Issued January 27, 1916 



AN ANALYSIS OF THE VERTEBRATE FAUNA 

 OF THE TRINITY REGION OF NORTH- 

 ERN CALIFORNIA 



BY 



JOSEPH GRINNELL 

 (Contribution from the Museum of Vertebrate Zoology of the University of California) 



From the array of facts presented in the foregoing paper (Kel- 

 logg, 1916), in conjunction with what is known of adjacent areas, 

 it seems possible to draw some general inferences as to the composi- 

 tion and derivation of the vertebrate fauna of the Trinity region. 

 Faunas vary through a wide range in degree of distinctness, from 

 that which is scarcely different from the one or ones adjacent, to 

 the fauna which is of marked peculiarity, showing throughout 

 nearly all its elements totally distinct characters. An example of 

 the latter would be the San Diegan fauna as compared with the 

 adjacent Colorado Desert fauna (see Grinnell and Swarth, 1913, 

 page 388). Of far less degree of difference, we may cite the Santa 

 Cruz faunal division of the Humid Coast Belt as compared with 

 the Marin division of the same belt. 



The difficulties arising in attempts to diagnose and properly 

 classify faunas are surprisingly similar to those encountered in 

 dealing with subspecies, species, genera and other systematic groups. 

 Not only is there such wide variability in amounts of difference 

 between faunas as to make the matter of rank often indeterminable, 

 but exact geographic boundaries may be impossible to fix because of 

 intergradation over intermediate territory of greater or less width. 

 As in some cases of intergrading series of subspecies, the location of 

 lines of separation may be subject only to arbitrary choice, so that 

 where six faunas might be recognized by one student, only three 

 would be thought properly distinguishable by another. 



