462 ZOOLOGY 



smaller claws, shaped like those of the Spermophiles. The hind soles are 

 entirely naked, without any conspicuous tubercles ; the heel is naked and 

 narrow. 



" These little sand rats," says Dr. Eichardson, " are numerous in the 

 neighborhood of Fort Vancouver, where they inhabit the declivities of low 

 hills, and burrow in the sandy soil. They feed on acorns, nuts {Gorylus 

 rostrata), and grass, and commit great havoc in the potato fields adjoining 

 the fort, not only by eating the potatoes on the spot, but by carrying off 

 large quantities of them in their pouches." 



The genus Saccomys is founded upon a North American Geomys. 

 The genus Perognathus was created for a new species inhabiting the 

 upper Missouri. The genus Heteromys contains two species ; one inhabits 

 Central America, the other Colombia and Guiana. The genera Macroco- 

 liis and Dijiodomys are Mexican, and include each only one species. 

 Dipodoinys phillipsii is the well known jumping or kangaroo rat of 

 California. 



Suh-fam, 2. Baihyergina^ composed only of the genera Bathyergus and 

 Georychus, the first with one, the second with two species, all three from 

 southern Africa. The Bathyergus capensis burrows in the sand flats of 

 the Cape of Good Hope in very great numbers. In every part of these flats 

 mole-hills are observed, and when walking on the surface the foot often 

 sinks into their galleries, thus making it very dangerous to ride on horse- 

 back in those localities, owing to the danger of being thrown by the unex- 

 pected sinking of the horse's feet into these holes. 



Sub-fam. 3. Arvicolma, have, like the rats {3Iurina\ three molars above 

 and below on each side, but rootless, each one being composed of triangular 

 prisms, placed on two alternate lines. 



The genus Arvicola includes the common field-rats, which have a hairy 

 cylindrical tail, shorter than the body, and the ears clothed with hair. The 

 fore feet have four toes and a rudimentary thumb; the hind feet are five- 

 toed, furnished with weak nails. They burrow in the earth and feed on 

 grain, bulbous roots, and grasses ; some are omnivorous, they do not climb, 

 are not dormant in winter, but seek their food during cold weather, eating 

 roots, grasses, and the bark of trees. 



The species of this genus are found all over the world ; nine of them 

 belong to North America. The meadow mouse or campagnol {A. pennsyl- 

 vanica) is very abundant in the northern and eastern United States, and 

 extends northwards as far as Hudson's Bay, and westwards to the banks 

 of the Ohio. It swims and dives well. A dozen more species are found in 

 North America ; some inhabit the Eastern States, others belong to the 

 western territories, Texas, Oregon, California, &c. 



The genus Lemm'm (the lemmings) includes those Arvicolina which 

 have very short ears and tails, and the toes of the fore feet adapted for 

 digging. There are five distinct nails to the fore feet. The species of 

 this genus are peculiar to the northern hemisphere. One of them, of the 

 size of a large rat, is celebrated for its occasional migrations in innumerable 

 bodies. At these periods they are said to march in a straight line, regard- 

 666 



