MQRlDiE— ARVICOLIN^E— ARVIOOLA RIPARIUS. 165 



Table XLI. — Measurements of sixteen specimens of A. rifarics from Northwestern States. 



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 scries is as 1.00 to 0.34, here it is as 1.00 to 0.37. 

 We also learn from this table of an interesting variability of proportionate 

 length of tail to body. Thus No. tWV, which is 3.50 long, and No. tttV, 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. 



