MDRIDJS -AltVICOLIN^— BVOTOMY8 RUTILUS GAPPERI. 143 



two tuMes gives an average difference between gapperi and true rutilus which 

 is readily appreciable; and most specimens are sufficiently marked to enable 

 us to assign tiiem to one or the other form with much confidence. We have 

 never seen a United States example that was not unmistakably gapperi, nor 

 un Arctic one not as evidently true rutilus. 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 liard 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 gapperi; but, in 1854, these gentlemen, finding their name "fulvus" 

 pre-occupied (by Lemmus fulvus Geoff., a French Arvkola), changed it to 

 dekayi. They gave an excellent and unmistakable description, and only err 

 in adducing ''^. oneida DeKay" as a synonym, the last being one of the 

 interminable designations of Aroicola riparius. 



This animal is so much like rutilus 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 rutilus 

 shows; the sides are not so luteous, being more yellowish brown, as in Arvi- 

 cola riparius for example, and underneath the iur 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 lies 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 rutilus the tail (vertebraj) is as 

 long OS the head, and tliat 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 



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