476 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
of the sides, and the latter is sometimes very pale yellowish-gray, &e. TI 
have observed no plumbeous or entirely gray stage like that frequently or 
usually seen in young Hesperomys ; and I have failed to determine what defi- 
nite relation, if any, the observable differences in coloration bear to sex 
or age. 
The animal varies much in size, and to some extent in proportions, 
especially the length of the tail. This is the most variable dimension, as 
usual in all such cases of high development of parts. A tendency to superior 
size in specimens from the Rocky Mountains and westward has been noted. 
The following table of measurements of an alcoholic series indicates very 
fairly the dimensions, and, to some extent, the variations in size and pro- 
portions :— 
TABLE I.— Measurements of twenty-one alcoholic specimens of ZAPUS HUDSONIUS. 
Skulls measure from 0.90 to 1.00 by 0.45 to 0.50. 
| 
2611 | West Northfield, Ill... 
2 e From tip of nose to— Tail— | Length of— 
o 
a cA Localit, 8 3 od 
as y- as = S S 
i - a 2 & iS 
ae Sect Peale Sho) Caan Di il eee ine 
A | A io) a a & a 
PE ING: CUTS et Nets Geena eo Seem SDSEnoo OSS OS acnSone se ones *0.45 0. 80 1.00 c 2.75 5. 00 0. 40 1.20 
2393) eMiddlebore! “Masse. 2-2-2 22- -4 asa nce eae eee 0. 42 0.75 1.00 2.90 5.29 0. 35 1.18 
0.45} 0.90} 1.00] 3.00] 5.00] 0.37] 1.20 
0, 42 0. 80 0.95. 2.75 4.50 0.45 1.18 
0. 40 0. 20 0.95 3. 60 ayn Basacse I edcaces: 
odie = 0. 43 0. 85 1.00 2.79 4.795 0,35 1.15 
2504) Burlinetony Vits-<=-.-- s-=0 cc encess<--eccmence= = aneeeeeen 0. 45 0. 90 1.00 3. 30 5.35 0. 40 1.18 
2599) |ioW ethéexsfield:|\Conn.)-02.,--c-c2ses soc So eee ese oeeeee 0.45 0. 20 1.00 2.75 4. 80 0. 40 1.10 
0.45 0. 80 1.00 2.75 4.35 0. 36 1.15 
0.45 0. 90 1.10 3.10 4.95 0.45 1.15 
0. 50 0.95 1.00 3.20 HU os siecscttessssass 
0. 45 0. 85 1,00 2. 85 4.90 0. 40 1.15 
0.45 0.90 1.00 3.00 5.00 0. 40 1.15 
O04) Pehigaelpwia see ssesesinecennsec= mete mae eae eeee 0.45 0. 85 1,00 2.90 4.65 0. 45 1.13 
SRGGL s Carlisle eo vane tana winco camera la ete ae ie ee eee 0.45 0. 85 1.€0 2. 85 4, 50 0. 45 1.15 
2602) |<... Goss eee 22 0. 45 0. 85 1.00 2. 85 4.75 0. 45 1.15 
2603 |....-. Ojos sea eee 0. 40 0. 80 0.95 2. 60 4. 40 0. 40 1,05 
4, 
2610) |) Upper Missourt River-c--.---.c-> ssosss en se tees eee eeee 0.50) 1.00 1.15 3.00 5. 
1929) (Platte River qNebrman--soucsce cess seceeace cee soe eeeeaae 0. 40 0. 80 0, 95 2.75: 4.50 0.45 1.12 
2609 | Steilacoom, W. T.-....-----..-- Sot och eeeor cn ean eee 0. 45 100))| 22s e4|ecee ee 6.10 0. 50 1.35 
Seat ose) S2eG2 S505 SS aaahesscgtaAcisessaos0 155 0.44 0. 86 0.99 2. 89 4.90 0, 42 1.15 
Average 
*All measurements are in English inches and decimals. 
GEOGRAPHICAL DISTRIBUTION. 
The dispersion of Zapus hudsonius in North America can at present be 
given only in somewhat general terms, pending precise information respect- 
