542 U. Ss. P, R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
its upper half by a broad, blunt nail. The first toe of the hind foot is short; its insertion far 
back and falling opposite to the middle of the foot, or even posterior to this point. The under 
half of the sole is hairy from the heel. The tail is rather long for species of this group; ex- 
clusive of the hairy tip, it is about one-third the length of the head and body; well covered 
with hairs to the tip. 
The upper fur is plumbeous from the base to near the tip, where the color deepens in intensity, 
and is succeeded abruptly by a yellowish brown tip. Interspersed are numerous hairs entirely 
black, which mix with the yellowish brown without obscuring or overshadowing it. This con- 
dition prevails on the upper parts and sides generally ; the side of the body being only a little 
less mixed with black. There is also a faint wash of darker rufous brown along the middle of 
the back. Beneath, the lead colored fur is tipped with pale rufous orcinnamon. The feet and 
tail above are brown, finely lined or streaked with pale rufous or cinnamon in less quantity 
than the brown. The tip of the tail is brown; its under parts like the belly. The sides of 
the muzzle and the tip of the chin are dark brown, but the bend of the lips is whitish. 
The skull is remarkable for its elongation, especially of the nasal portion. It is just twice © 
as long as broad, measuring 1.12 by 56, or as 100 to 50. The nasal branches of the intermax- 
illary extend backward beyond the lachrymals, and exceed the truncated extremity of the nasal 
bones by one-tenth of an inch. The distance from the anterior extremity of the line of upper 
molars to the posterior base of incisors is more than one-third the distance from the incisors to 
the occiput (.37 to 1.05). The line of upper molars is short, (.27,) or about 24 hundredths 
the total length. The nasal bones measure .33 of an inch, or .294 of the total length. 
The posterior upper molar has three salient angles on both the exterior and interior sides; 
the posterior outer, however, is quite small, and even almost obsolete. The indentations of 
enamel are such as not to cut off any lateral triangles, there being one anterior and one middle 
one going entirely across the tooth, instead of an anterior and an exterior and interior. There 
is also the usual posterior loop. The anterior lower molar has one posterior closed triangle, 
two interior, one exterior, and an anterior lobe with an indentation in each side, making five 
internal salient angles, four external ones, and an anterior loop. 
Judging from the skin alone, it would be rather hazardous to establish this Arvicola as dis? 
tinct from A. austera, the external differences being but slight. The skull, however, has 
several peculiarities which I have not observed in a considerable number of specimens ; none of 
those in the collection from Wisconsin, Illinois, Missouri, or Louisiana, sharing them in any 
way, although varying considerably among themselves. The rudimentary thumb nail is armed 
with a nail rather larger than usual, being, in fact, like one of the other claws, with the point 
worn off bluntly, and not continuous beneath nor enveloping the phalanx below. The tail is 
longer than in the others; with the hairs, measuring over 14 inch, or one-third the length of the 
head and body ; it is thinner than in all the allied species. The ears are smaller. The cin- 
namon of the under parts is rather deeper, as is the brown about the muzzle. 
The points in which the skull of this specimen differs from those of A. austera are the nar- 
rowness compared with the length (one-half); the elongation of the nasal bones, and of the 
muzzle generally ; the shortness of the lines of molars; the absence of any lateral triangles in 
the posterior upper molar, &c. 
