538 MONOGRAPHS OF NORTH 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 speeimens 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 disfinction 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 redative 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 ¢wice 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 Dipopomys. 
ROCKY MOUNTAIN REGION. > PACIFIC COAST REGION. 
ere lene eral | ee |e 
2S/Bu) 8 @€5/5</ 6 
2 ) rs co =} = 
q > sa} q > ioe) 
ATI ZON Rivero s]<saafaete omer es ase hice siete 4.25 | 5.00 | 1.55 | Cape St. Lucas..............-.----------- 3.50 | 5.00 | 1.35 
We esecasageeenco SHES SOAS sme emece ASO) os eo | eas hetemtere GO) oss ace ceeeieie em ce. heme ees 3.50 | 5.25 | 1.40 
New MOxiC0 iis 4)- Fann aoaemsveeeet clenmees 4.50 | 5.00 | 1.55] ..... POyeceer=-saee 3.75 | 5,75 | 1.40 
Platte Walley. .-sccscsos cece caaseccans pe BE es || TRESS | esaine do == 3.75 | 5.75 | 1.40 
nee do 3.75 | 5.75 | 1.45 
Fort Reading, 3.35 | 5.80 | 1.60 
ED |< ea et ne gH ee |e Gites Re naqckeoscecc era sSoeacesec: 3.25 | 6.00 | 1.60 
Monterey jac <<)t-ean nena ee eon 5.00 | 6.75 | 1.70 
Fort Tejon, (OF) Pee eRe esicetctosascorr 4.25 | 7.00 | 1.70 
AV OLAP CS pene sjeerece\teanen cece: | 4043) (5).25.'| LO3 i) a coc~ cies ta ploc cee eeee eae eaeee nee see eee 3.78 | 5.89 | 1.51 
