486 vu. Ss. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
NEOTOMA, Say and Ord. 
Neotoma, Say & Orv, J. A. N. Sc. Phila. IV, 11, 1825, 346, 
Aup. & Bacu. N. Am. Quad. I, 1849, 31. 
Form closely rat-like. Tail long, more or less densely hairy. Ears very large, nearly naked. Molars rooted, teeth 
strongly arvicoline, composed partly of straight-sided triangles. Heels hairy. 
The genus Neotoma is peculiarly North American, and occurs throughout the whole United 
States, excepting the New England States. It embraces very large species, some of them 
greatly exceeding the house rats in size, and much superior to them in beauty and docility. 
One species (N. magister) occurs fossil in the caves of Pennsylvania. 
The fur of the species is soft and very full in the bushy-tailed species. The ears are very 
large, as are the eyes, exceeding, in this respect, the house rats. 
The molars are all rooted ; their grinding surfaces plane, whether tuberculate in the young 
has not yet been ascertained. They are narrow, those of either jaw of nearly equal width 
among themselves, (the lower narrower.) Above, they diminish progressively from the first, the 
last, two-thirds as large as the first. Below, the first two, are equal, the last, two-thirds as long. 
The upper molars have each two indentations or re-entrant loops of enamel on the outer side; 
the first or anterior one has two on the inside, the other two but one. The additional inner 
one of the first molar is very shallow, situated far forward, and, in fact, is a mere indentation 
in what would otherwise correspond to the anterior triangle of the other teeth, the pattern of 
all three being otherwise quite similar. Here, as in Sigmodon, the re-entrant enamel loops of 
two sides of a tooth which are nearly opposite each other, come into actual contact, and the 
hinder outer one extends across to the opposite side, completely separating the dentine into 
three islands. In the lower jaw there are two re-entrant angles on the outside of the first and 
second, three on the inside of the first, two of the second, the third has one on either side. 
The anterior inner indentation of the first molar is much like that on the upper first molar ; 
all the re-entering loops on opposite sides are in the same line and touch each other, the indica- 
tion of alternation being scarcely discernible. 
The loops, both salient and re-entrant, of both jaws, are quite acute, scarcely rounded, the 
edges or sides, especially the posterior limb of the external upper loops, nearly straight. In 
fact, a line drawn longitudinally down the crowns of the teeth would divide them into a series 
of triangles, especially in the lower jaw, where the opposite ones would be placed nearly base 
to base. : 
The molars of Neotoma have the enamel folds somewhat like those of Sigmodon, in the upper 
jaw, excepting that the angles and lines are more rounded. The lower teeth differ much more ; 
thus the second molar has two indentations on either side, opposite each other in the one, while 
Sigmodon has but one, alternating. The teeth of Neotoma are longer, narrower, the sides more 
parallel, and the salient lobes more divaricated. 
There are two very strongly marked sections of Neotoma: one with the tail short haired and 
not more conspicuously hairy than in the common rats, with short snout; the other with a very full 
densely haired, even bushy, tail, very long muzzle, &c. To the first belong N. floridana, 
micropus, mexicana, and fuscipes; to the other, N. cinerea and occidentalis. There are very 
striking differences in the skulls, which, in the bushy-tailed species, have the muzzle greatly 
