58 Miller — Description of a Netu Wldte-Footed Mouse 



specimens (of "JET. leucopas''^) have the tail vertebra) equal to or 

 lonj^er than the head and body. * * * At least four-fifths, 

 liowever, have the tail shorter than the head and body, and 

 occasionally one occurs with the tail only equal to the body 

 alone. In these latter the proportional length of the tail ver- 

 tebrfB to the length of the head and body is as 68 to 100 ; in the 

 other extreme, or in those with long tails, as 118 to 100. The 

 variation between these extremes is hence fifty per cent, of the 

 mean — a striking example of the unreliability of this character 

 as a specific distinction. * * * " 



Dr. Coues repeats Mr. Allen's observations, adding: '' Tbe 

 variation in absolute and relative length of the tail is greater 

 tlian in any other dimension, -i^ * * But this ceases to be 

 remarkable when we recollect that it is purely a matter of what 

 has been aptly called ' vegetative repetition.' It seems to l)e a 

 well-nigh universal law that those parts or organs that are least 

 specialized — L e., those of which several have the same or corre- 

 sponding character and function — are liable to be produced with 

 a high degree of irregularity as regard their number, and the 

 more such there are the wider are the limits of variation apt to 

 be. In this species, one of our longest-tailed rodents, the law is 

 perfectly illustrated." 



A glance at the appended ta]:)lcs of measurements and ratios 

 of two hundred and fifty white-footed mice from the eastern 

 United States and adjoining British provinces will show the in- 

 correctness of the views quoted above. The range of variation 

 in ratio of tail vertebne to total length is in *S*. americanus from 

 about 40 to a])0ut 48, while in tlie longer-tailed S. a. canadensis 

 the variation is from 47.4 to 54.2. That Dr. Coues and Mr. 

 Allen should have ftillen into this error is probably due to tlie 

 fact that their measurements were taken in part from distorted 

 skins or alcoholic specimens, and also to the confusion of the 

 two races under one name. The measuren>ents here talndated 

 were all taken from the fresh specimens before skinning, and, 

 unless otherwise stated, the writer is responsible for their accu- 

 racy. 



»So many names have l)een i)roposed for white-footed mice 

 from eastern North America that it may appear somewhat haz- 

 ardous to institute still another; hence the species described 

 by authors from the region of importance in the present con- 

 nection may well be considered here in some detail. 



