THE MOUSE TRIBE. 127 
stores for winter use. These stores are generally accumulated in hollow trees or 
logs, and sometimes may contain two or three quarts of beech-nuts or clover-seed. 
This mouse, unlike the hamster, remains, however, active throughout the winter ; 
and may be seen running about on the snow, where its long tail leaves a character- 
istic track. It is an agile climber, running up tree-stems with the activity of a 
squirrel, and frequently disappearing in some hole at a great distance above the 
ground. In addition to nuts and seeds, the white-footed mouse will readily eat 
the flesh of such animals as come in its way, and it is possible that it may occasion- 
ally kill small birds for itself. From three to six young are produced at a birth, 
and there appear to be several litters during the year. The first coat of the young 
is of a uniform dull grey colour. In the northern portions of the range of this 
mouse, the nest is generally built either in the hollow of a tree or a log, or ina 
burrow ; but more to the south these animals construct an “outside nest” of moss, 
grass, leaves, or bark, which is generally more or less cocoanut-shaped, and may be 
as much as a foot in diameter. It is usually suspended from a horizontal branch 
at some distance from the ground, and has its entrance on the under surface. The 
group to which this particular species of white-footed mice belongs is distinguished 
by having only five tubercles on the first molar tooth in the upper jaw. The rice- 
field mouse (C. palustris), which attains the size of a small rat, does much damage 
to the rice crops in the Southern States. 
THe FisH-EatTine Rat. 
Genus Ichthyonys. 
A remarkable species (J. stolzmanni) inhabiting the mountain-streams of 
central Peru is allied to the preceding group, but distinguished by its aquatic and 
probably fish-eating habits, as well as by its webbed and fringed hind-feet. In 
size it comes near the brown rat, but has the head much flattened, larger whiskers, 
and very small ears and eyes; while in colour it is dark above and whitish 
beneath, with a black-and-white tail. 
THE GROOVED-TOOTHED MICE. 
Genera Rhithrodontomys and Rhithrodon. 
Two groups of American Cricetines are distinguished by their upper incisor 
teeth being marked by parallel grooves. Of these, the American harvest-mouse 
(Rhithrodontomys humilis) resembles the rice-field mouse in external appearance, 
and is found in the southern United States as far north as Iowa; the two other 
species of the genus being also North American. 
The Rhithrodonts, on the other hand, are exclusively South American, and 
are characterised by their rabbit-like appearance, the head being very short, with 
a highly convex profile, very large eyes, and rather large rounded ears. The 
rabbit-like rhithrodon (Rhithrodon cuniculoides), from Patagonia, is one of the 
best known species. The length of the head and body is 64 inches, and that of 
