370 FRANCIS B. SUMNER 



been dealt with in previous reports. A further character of 

 great importance, which I plan to study quantitatively, is the 

 color of the pelage, but no data from this source will be considered 

 in the present paper. ^ 



1 shall not regard it as necessary here to discuss either the 

 technique followed in making the measurements or the methods 

 employed in the subsequent statistical treatment. Some of my 

 former papers have covered this ground sufficiently well for 

 present purposes. 



To reverse the conventional procedure, I propose here to sum- 

 marize and discuss my results in advance of the more detailed 

 account. This will serve to make clear at the outset the purpose 

 of the paper, and will perhaps render the detailed statements 

 more intelligible to such readers as may stray beyond this 

 introduction. 



To proceed with this general discussion, significant racial dif- 

 ferences have been found in respect to the mean length of the 

 tail, foot, ear, pelvis, femur, and skull, the width of the dorsal 

 tail stripe, the color of the pelage, depth of pigmentation of the 

 foot, and number of vertebrae in the tail. There are not, how- 

 ever, for any one character, as many grades to be distinguished 

 as there are localities from which collections have been made. 

 For example, I have thus far found only six distinguishable 

 grades in respect to tail length and only four or five in respect to 

 foot length. 



Local collections from different parts of the ranges of the same 

 'subspecies,' as thus far recognized by systematists, have been 

 found to differ considerably. Thus, the two extremes, in re- 

 spect to ear length, are presented by the Berkeley and the La 

 Jolla collections, both of which are generally assigned^ to the 

 subspecies 'gambeli,' while the subspecies 'rubidus,' as regards 

 several characters, presents at least three well-marked grada- 



2 Mr. H. H. Collins is preparing a paper which includes color analyses made in 

 accordance with a method which we have developed jointly. 



3 Stephens (California Mammals, San Diego, 1906) ; Osgood (Revision of Mice 

 of the American genus Peromyscus, Bureau of Biological Survey, Washington, 

 1909) ; Grinnell (Distributional List of the Mammals of California, Proceedings 

 California Academy of Sciences, August 28, 1913). 



