460 U. 8. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
Sp. Cx.—Young, dark slaty plumbeous. Adult, yellowish brown; most usually a broad and well defined dorsal wash of 
darker. Tail pure white beneath. Tail nearly as long as head and body. Posterior tubercle of sole large, elongated. 
Soles hairy for less than half their length. Ears with the edge only lighter. Maximum size of body, in the flesh, 3. 60; 
hind feet, .75 to.85. Maximum of skull, 1. 05 inches; in one instance, 1. 07. 
This animal is considerably larger than the common domestic mouse, the head and body 
broader also in proportion. The more varied colors, longer and softer fur, larger ears and eyes, 
and external appearance generally, give to it a much more attractive appearance than that 
presented by the house mouse. In localities where the latter species has not yet penetrated, it 
often takes up its abode in dwellings and out-buildings, infesting the premises and doing all 
the petty mischief for which the other species is so well known. 
The head of this animal is rather broad in proportion to its length. The muffle is entirely 
hairy to the extremity, both above and below, the septum and region around the nostrils alone 
‘being naked. The hair even extends in an obtuse angle a little way on to the septum, but not 
reaching the level of the nostrils. The nostrils are elliptical, and partly visible from the side. 
The septum is rather wide, with a single median separating furrow, which passes directly into 
the deep fissure of the upper lip. This fissure extends as far as the nose, becoming more and 
moreshallow. No traces of cheek pouches can be detected. The ears are large and rounded. 
There is a long low antitragus, which, however, does not appear at all valvular, as in Jaculus 
and perhaps feithredon. It is thinly coated with hairs on both sides, except around the 
meatus. : 
The thumb of the fore finger is a very rudimentary callosity, covered with a broad flat nail 
exactly resembling that on the human hand. The third finger is longest; the fourth but little 
shorter ; the second and fifth successively shorter still. The proportions of the hind toes are 
much like those of the fingers ; the first toe is, however, longer, its claw not reaching quite to 
the penultimate articulation of the second toe. The palms are naked, with five large nearly 
equal tubercles, which nearly cover them ; the soles have six tubercles, ‘the anterior five quite 
similar in size and position to those of the hands, the posterior single one placed a little 
anterior to a point midway between the heel and the bases of the toes. The soles are covered 
with short hairs from the heel to near the first tubercle. This character will always serve to 
distinguish the white-footed mouse from the common domestic mouse, in which the entire under 
surface of the sole is perfectly naked. 
The tail is a little shorter than the head and body ; very rarely attaining the same size or 
longer ; it is rounded, tapering to a rather blunt tip; its surface covered with whorls of scales, 
between which spring short hairs, partially concealing them; the tail appearing considerably 
more hairy than in the domestic mouse. 
The colors of this animal vary very considerably with age. The most perfect pelage of the 
fully adult specimens is of a light yellowish brown color on the back and sides; the middle 
of the back, along a space about the width of the head between the ears, having a wash of 
darker, owing to a predominance of blackish tips to the hairs; these tips are also seen on the 
sides, but in less amount. In some specimens there is a faint indication of a lateral stripe of 
quite bright rusty yellowish extending on to the cheeks. The under parts and insides of the 
limbs, with the upper surfaces of the feet, are pure cottony white. The line of demarcation 
between the colors of the belly and sides commences at the upper incisors, passes backward 
under the eye, over the shoulders, and along the middle of the sides to the outer edge of the 
hind legs. The outer surface of the hind legs, exclusive of the feet, is always colored like the 
