138 NORTHERN ZOOLOGY. 
bushy tail, densely hairy, instead of a round tapering one, scaly and thinly hairy. 
In the softness of its fur, and general arrangement of its colours, it has much 
similarity to the common wood-rat. It differs, however, from the genus mus, as 
now restricted, in the form of its teeth, approaching more nearly to the genus 
arvicola in that respect than to any other, but receding from it, on the other hand, 
in the length of its tail, limbs, and in its general light, active form. Besides the 
specimen brought home by the Expedition, and from which the accompanying 
very correct engraving by lLandseer was executed, there is another good 
specimen in the Museum of the Hudson’s Bay Company ; a third, with a mutilated 
tail, in the Zoological Museum; and a fourth, without a tail, and much over- 
stuffed, in the British Museum, all said to have come from the same quarter. I 
have also a hunter’s skin, of a larger, and perhaps a specifically distinct kind, 
procured on the Rocky Mountains in latitude 63°. 
DESCRIPTION. 
In size, this Neotoma equals the Norway rat, and it has a good deal of the character of 
that animal in its physiognomy. Its nose is compressed and narrow, but appears rather 
obtuse if viewed laterally. There is a very narrow, naked margin to the nostrils, the tip and 
sides of the nose being covered with short hairs. The upper lip is divided about three 
lines deep. 
Dental formula, incisors 2, canines =}, grinders = = 16. 
The incisors have precisely the form of those of the meadow-mice, and wear away in the 
same manner at their points. The upper ones are short, slightly rounded, and not grooved 
on their anterior surface. The lower ones are long, narrow, and rounded anteriorly and 
on the sides. The molar teeth also very much resemble those of a meadow-mouse. (2, 
santhognathus). The grooves on their sides, however, instead of running to the base of 
the tooth, terminate abruptly, where it is immersed in the socket; and some little distance 
below this termination, most of the grinders divide into two fangs. The two anterior pairs 
of lower grinders have these fangs very distinct, the space between the fangs being deep 
and wide; but the upper grinders and the posterior pair in the lower jaw have them much 
shorter, and as it were coalesced. The first grinder in the upper jaw has the rudiments of 
three fangs. The grinders of both jaws have a slight inclination backwards, and they gradually 
decrease from before backwards in size, and in the height of the part which projects above 
the sockets, preserving however an even grinding surface. In the upper jaw, the first 
grinder has three grooves on its exterior side, and as many inside, with an equal number of 
rounded projecting columns or ribs of a side; the second and third grinders have each two 
grooves, with three ribs exteriorly, and one groove with two ribs interiorly. In all, there 
are nine ribs on the exterior sides of the upper rows of grinders, seven on the interior sides, 
