MURIDH—ARVICOLINZE—ARVICOLA RIPARIUS. 165 
TaBLe XLI.—Measurements of sixteen specimens of A. riparics from Northwestern States. 
| Tail to end 
Eat 
Ss | 
if— & 
g Date. Locality. Collected by— i —- fo 
= - = = - Ee 
Bae Be oases 
pettus. teu Mal 140 | 3.50| 1.60] 0.36 | 0.7 
eeeiensseeed 1.60 | 3.59 | 1.40 | 0.37 | 0.8% 
MWececeaecetsats 1.90 | 4.00 | L. 70 | 0.33 | O35 
.| Spring, 1855 1.40 | 3.75 | 1.30 | 0.39 | 0.78 
Jan. —. 1855 1.60 | 4.25 | 1.45 | 0.38 | 0.81 
Spring. 0855! |. --ccdOL oc easo seek acer acto oe | Mec ee Oe see nee een eee 4.35 ieee 0.40 | 0.85 
Sed Pose Scere od) Beer ret) Oso noone ae ee eCO Cogs reeee: UO seemec Sosa Cosme son ok [eee 3. 85 Jnor-- 0.38 | 0. 84 
f°) 1.70 | 4.50 | 1.59 | 0.37 | 0.80 | 
Q 1.55 | 4.20 | 1.45 | 0.36 | 0.75 
o 1.85 | 4.40 | 1.70 | 0.39 | 0.80 
S 1,70 | 3.75 | 1.50 | 0.33 | 0.85 
Boll ocean saeaast 1.45 | 4.25 | 1.25 | 0.34 | 0.76 
-.| July 16, 1853 1.20 | 4.45 | 1.55 | 0.38] 0.£0 | 
Al : 1.40 | 4.00 | 1.35 | 0.35 | 0.78 | 
rol Detroit, Mich 255 ...| 1.85 | 4.50 | 1.60 | 0.38 | 0.20 | 
Q | Aug. —, 1853} Detroit River, Mich .........- Prof. ’S.ctenind oa 5o. eee 1.75 | 3.50 | 1.50] 0.37 | 0.€0 | 
| 
ASV OTe soe oe sxe ET ae ee en ..-.| 4.04 | 1:49) |e 22 0.79 | 
These measurements are nearly all from dried skins, which nevertheless 
are so well prepared that there is no appreciable source of error. The aver- 
age—barely, over 4.00—is less than that of the Philadelphia series by about 
three-tenths of an inch, while the tails average rather more. While the 
proportion in the eastern series is as 1.00 to 0.34, here it is as 1.00 to 0.37. 
We also learn from this table of anv interesting variability of proportionate 
length of tail to body. Thus No. 7%, which is 3.50 long, and No. y1z, 4.50 
long, both have the same length of tail, 1.60; in the former the proportion is 
1.00 to 0.46, and in the latter 1.C0 to 0.36; that is to say, the tail may 
vary in specimens from substantially the same locality, from but little over 
one-third to nearly one-half the length of the trunk. The hind feet remain 
substantially the same as in the two preceding series (being slightly larger 
than the Philadelphia one and slightly smaller than the Massachusetts one), 
which, with the decrease in total stature, gives relatively a little larger foot 
of these specimens. In animals, then, from the Upper Mississippi Valley, 
we see a slight decrease in average stature, associated with a little longer 
(relatively) tail and hind feet. We desire it to be observed, for purposes of 
certain comparisons instituted beyond, that we have not yet seen any hind 
foot touch 0.90 in length, none exceeding, and but few reaching, 0.85. 
