RODENTIA—ARVICOLINAE—ARYVICOLA HAYDENII. 543 
List of specimens. 
= Measurements. 
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591? | 1714 | Pembina, Minn..... cece! C. Cavileer ......cceees Skin ...... 1.25 | 4.50} 1.42 | 1.66 |......|s..00. 1.13 | .57|......| Fresh ..soue 
eecees 4.20 | 1.30} 1.50] .40| .79|.....-Jecceee 40 | Skin ....006 
+ Measured before skinning. 
ARVICOLA (PEDOMYS) HAYDENII, Baird. 
Sp. Cu.—Larger than A. austera. Length, 4} inches. 
feet. Fur coarse, half an inch long above. 
Feet broad; sole hairy for half its length. 
Tail vertebra one third this length; not quite twice the hind 
Ears short, half as long as hind foot; sparsely furred with longish hairs 
Above, yellowish brown, uniformly mixed with black; the whole with a gray tint. Sides grayer and with less black. 
Beneath, grayish white without any cinnamon. Line separating the sides and belly distinct; cheeks light colored. Tail 
sharply bicolor ; colored in correspondence with the body. Plumbeous of fur deepening just before the brown tip. Skull 
1.14 by .65, or as 100 to 57. 
This species is amongst the largest of those occurring within the limits of the United States. 
The head is broad and rather obtuse. The whiskers are shorter than the head, black and gray. 
The ears are short, almost broader than long, rather sparsely covered with long hairs on both 
sides, except around the meatus; the antitragus large and semi-circular. The feet are stout, 
rather large ; the nail-like claw of the rudimentary thumb well developed. The sole is hairy ° 
beneath for half its length from the heel ; the insertion of the first toe is opposite the centre of 
the foot. The tail is short, about one-third as long as the head and body, tapering to a slight 
pencil at tip, and coated with stiff hairs throughout. 
The hair is quite coarse and bristly, especially about the head; on the back it measures about 
half an inch ; half as much on the under surface. 
The fur is plumbeous from the base to near the tip, where there is a penultimate deepening 
in color, succeeded by a tip of yellowish brown. This being relieved by black tipped hairs 
gives a uniformly mixed color above, the prevailing tint of which is a grayish yellowish brown. 
The sides are grayer and less mixed with black. The under fur is broadly tipped with grayish 
yellow white, having a tinge of pale yellowish rusty across the belly. There is, however, no 
trace of cinnamon. The feet are pale rusty yellowish white above, with a few black hairs; the 
tail above is brown ; beneath, like the belly, with a very distinct separation. 
The skull resembles more Arvicola austera in shape than A. cinnamonea, although the con- 
traction of the interorbital portion does not extend so far back, falling anterior to the central 
point of the skull. The distance from the anterior extremity of the upper molars to the pos- 
terior base of the upper incisors is one-third that from the incisors to the occiput. The line of 
upper molars measures .25 of an inch, or .22 of the total length. The posterior upper molar 
has an anterior triangle, next one exterior, next one interior, and behind these a broad V-shaped 
loop, with concave exteriors, The lower jaw is very massive; the anterior molar with one 
