538 



MONOGRAPHS OF NORTn AMERICAN RODENTIA. 



of geographical limitations; for the specimens which are arranged in the 

 table with reference! to absolute length of tail vertebrae (with which absolute 

 length of feet is approximately correspondent) show complete intermixture 

 of localities. Measurements of a hundred or a thousand specimens would, 

 of course, only tend to place these facts in stronger light. It may be safely 

 stated as a fact, then, that differences in absolute size, either of the body or 

 of any of its members, are not available for distinction of two species; and, 

 furthermore, that no set of absolute dimensions is correlated with geographi- 

 cal distribution. 



Nevertheless, one cannot fail to be struck, in examining the table, with 

 the extraordinary discrepancy in relative length of the body and tail. In No. 

 4871, for example, the tail (vertebrae) is only half an inch longer than the 

 head and body (4.50-5.00); that is to say, it is but one-ninth of the head and 

 body length longer. In No. 2626, the tail is two and three-quarter inches 

 longer than the head and body; that is to say, almost twice as long. It would 

 appear improbable that such unusual difference as this should not signify 

 something more than mere individual variability. In order to discover 

 whether or not the proportionate (as distinguished from absolute) dimensions 

 of body and tail may not lead to some tangible result, the following table is 

 constructed, in which the same specimens are arranged geographically. It is 

 necessary to exclude four of them, however — Nos. &478, 7349, from unknown 

 localities, together with the two respectively marked "California" and "Rocky 

 Mts.", as I have reason to believe that these indications of locality are not 

 reliable. 



Table VI. — Measurements of thirteen specimens of Dipodomvs. 



HOCKY MOUNTAIN REUION. 



PACIFIC COAST REGION. 



Arizona 



!>.. 



Now Mexico . 

 I'lalto Valley 



Averages . 



w 



4.25 

 4.50 

 4.50 

 4.50 





5.00 

 5.25 

 5.00 



5.75 



4. 43 5. 25 



1.55 

 1.50 

 1.55 

 1.55 



Cape St. Lucas 



do 



do 



do 



do 



Fort Reading, Cal. 



do 



Monterey 



Fort Tejon, Cal... 



1 s 

 w 



3.50 

 3.50 



:i. 75 



3.75 

 3.75 

 3.35 

 3.25 

 5.00 

 4.25 



5.00 

 5.25 

 5. (5 

 5.75 

 5.75 

 5.80 

 6.00 

 0.75 

 7.00 



5. 89 



w 



1.35 

 1.40 



1.40 

 1.40 

 1.45 



1.00 

 1.00 

 1.7U 

 1.70 



