MURIDA—SIGMODON'TES—H. LEUCOPUS SONORIENSIS. 83 
We will next show that the short-tailedness ot var. sonoriensis likewise 
characterizes, almost unexceptionally, the mice of Arctic North America. 
Indeed, this fact has already been shown in the previous table, which we intro- 
duced to settle the myoides question; these additional specimens, indeed, 
are merely the rest of our Arctic lot, positively the same as those of the 
‘“‘myoides” table. Most of these Arctic ones are noticeably larger than United 
States specimens, as was to have been expected; they average about 3.66 in 
length, with tail about 2.75; while the relative lengths of tail and body of 
sonoriensis are nearly repeated, about half an inch has been added to the abso- 
lute lengths of both trunk and tail. The feet are rather smaller, both abso- 
lutely and relatively, than in true dewcopus, averaging only 0.75, notwithstanding 
the increase of general size. This feature, as well as the shortness of the tail, 
might be explained upon the well-known law of smallness of peripheral parts 
in Arctic animals; but it is curious that it should correspond exactly with the 
shortness of tail of the New Mexican animals, which, of course, are not 
amenable to this law. The tail and feet are both unusually hairy. Here is 
the table: — 
TaBLE XX.—Measurements of sixty-nine (and list of other) additional specimens of British American and Arctic 
HESPEROMYS LEUCOPUS, mostly of the ‘‘ sonoriensis” style. 
{Not much reliance can be placed on the dry measurements, as the skins are all badly prepared, being almost without 
exception overstuffed, the tails being skinned aud distorted, and the feet having the toes curled up.] 
Nose to— pairerend 
: #/ 3 
Locality. Collector. = : s = Remarks. 
A|/A|/olal|r> | A/a] a] @ 
L. Clarke, jr - --- | . 25 | 2.50 }......]..---.| 0.80} .----. Dry. 
se5 PAIS TU ersscl Beene LN) Re --do, 
Seed peerage | Sr eae --do. 
SELLS Nica ate [esate etl omy | hrrerereee ..do, 
CAE WW eer feeceee! (a ere! eer ---do. 
2.40 |. ----.|--..~.)| 0.80) --do, 
Spay eee lece en METH EReaee --do. 
200) | Samael eemees 0410) cones --do. 
PW) ee nn} URE OH fe ee --do. 
PES] ese a esas) Pi (i) ec -.do. 
OU ON emo eeseoy i SY ir fal beeen --do. 
OF S8Nal ee sapere OaB|cacaee - do. 
2.00 |-----.|......! O79 |.-..2. --do. 
cece } SoaewaleassQOs 
CET ey seo ONT0) [pean do. 
2B W eeeeed pcos Wc |e do. 
PAG ase SIR a6 HO,00))| =< ---do. 
Bence ecmed te esce Ui 2} ee do 
S100 )|\esaee| seen arn (Bi Pea do. 
2A) BSA at Pal a = UScel Soeens base do 
