MURIDAS —ARVICOLINAX—EVOTOMYS RUTILUS GAPPERI. 143 
two tables gives an average difference between gapperi and true rutilus which 
is readily appreciable; and most specimens are sufficiently marked to enable 
us to assign them to one or the other form with much confidence. We have 
never seen a United States example that was not unmistakably gapperi, nor 
an Arctic one not as evidently true ruti/us. But the two forms dovetail so 
nicely that they cannot possibly be specifically separated; and, moreover, we 
are unable to assign the geographical limits of either with greater precision 
than is given in the opening paragraph under the heading. Mr. Kennicott’s 
Red River specimens appear to be gapperi, but stand hard against rutilus. 
The Fort Churchill animal, although so northern, is one of the longest-tailed 
of the whole series. 
Regarding the name of this southern form, there is little or no question. 
As we have shown, the long-tailed and -footed forms extend a little north of 
the United States; Nova Scotian examples, for instance, are truly like those 
of the United States, and so are others from the Red River of the North. 
Gapper’s animal was from Canada, and therefore quite within the known 
range of the southern form. In 1842, the United States style was renamed 
“fulvus” by Audubon and Bachman, probably in ignorance of Vigors’s pre- 
vious name gapperz; but, in 1854, these gentlemen, finding their name “fulvus” 
pre-occupied (by Lemmus fulvus Geoff., a French Arvicola), changed it to 
dekayi. ‘They gave an excellent and unmistakable description, and only err 
in adducing ‘“(A. oneida DeKay” as a synonym, the last being one of the 
interminable designations of Arvicola riparius. 
This animal is so much like ruti/us that we can only characterize it in 
comparative terms. Possibly it ranges a trifle larger; but the difference is 
never very evident, and often none exists. In color, it runs a little darker, we 
believe ; that is to say, the upper parts are more strongly chestnut rather than 
yellowish ferrugineous, lacking the “red” or ‘ orange” shade that ruti/us 
shows; the sides are not so luteous, being more yellowish-brown, as in Arvi- 
cola riparius for example, and underneath the fur is simply grayish-ashy-white, 
instead of having a strong clay-colored cast. Generally, the feet are less 
purely white; a difference in the length and thickness of the fur is notice- 
able. But the chief discrepancy les in the relative and absolute length 
of the feet and tail, especially the latter. Without professing to draw an 
infallible dividing line, we may say that in true rutidus the tat’(vertebra) is as 
long as the head, and that in gapperi it is longer. In either case, it is, with 
the hairs, about twice as long as the sole; but then it must be remembered 
