MAMMALIA. 139 
and ten triangles, formed by the folds of enamel on their crowns. In the lower jaw, the first 
grinder has two grooves exteriorly, and three interiorly ; the second has two grooves on each 
side, and the third, one on each side. In all, there are nine ribs on the outsides, and eight on 
the insides of the lower rows of grinders, and nine triangular folds of enamel on their crowns. 
These triangles are disposed in a single series, or at least present, very obscurely, the double 
alternate arrangement which exists on the crowns of the grinders-of the meadow-mice. The 
grinders of a Neotoma further differ from those of the meadow-mice in the ribs on their sides 
being broader and more rounded, and in the first upper grinder, instead of the last one, being 
the largest. The whiskers are considerably longer than the head; the anterior ones are 
white ; the posterior ones, which are longer and stronger, are black, more or less tipped 
with white. The ears are large, oval, and rounded, closely covered on the back with 
short, adpressed, blackish-gray hairs, and they have a very narrow and obscure white margin. 
Their anterior surface is more sparingly hairy above, and is quite naked near the auditory 
opening. , 
The fur is remarkably fine, soft, and long, and has considerable lustre. The upper parts, 
including the head and cheeks, back, sides, and outer surface of the fore and hind thighs and 
legs, have a nearly uniform, light, yellowish-brown colour, intimately mixed with black hairs; 
the resulting tint is between a hair-brown anda fawn colour. The black hairs are more 
abundant on the sides of the nose, down the middle of the head and back, and about the 
rump. The upper lip, chin, throat, all the under parts, the inside of the thighs, and the 
whole of the feet, from the wrist and ankle joints, are pure white. The fur is longest on 
the back and sides, a little shorter on the belly, and shortest about the nose, but the furry 
coat is close throughout, and is everywhere of a deep blackish-gray colour for two-thirds 
of its length from the roots. 
The tail at its commencement is cylindrical, and clothed with shorter hairs; but the fur 
gradually lengthens towards its extremity, where it is upwards of an inch long, and is 
somewhat distichously arranged, particularly beneath. The whole of the fur of the tail is 
very close and woolly at bottom. Fora short space next the rump, the tail is coloured above 
like the back; but for the greatest part of its length it is of a dark lead-gray, arising from 
an intimate intermixture of blackish-gray and whitish hairs. Underneath it is throughout of 
a white colour, and when the tail is spread out, the white hairs form to it an indistinct 
white tip. 
The feet are thickly clothed above with fur, which conceals the claws. On the fore-feet 
there are four toes, which do not differ much from each other in length, the two middle ones 
being longer only in a very slight degree. There is a small callus in place of a thumb, which 
is situated behind the roots of the toes, and is protected by a minute adpressed nail. There 
are besides five callous eminences of considerable size on the palm; three arranged in a 
triangular form at the roots of the toes, one a little longer posterior to the thumb tubercle, 
and another of equal size opposite to it. The claws are white, short, much curved, and 
very acute. The hind-feet have five toes, the four anterior of which much resemble those 
T 2 
