MAMMALOGY AND ORNITHOLOGY. 269' 



in eacli jaw; they are large and powerful, and provided with sharp, cutting, 

 chisel-shaped edges, adapted to gnawing. The constant severe action to which 

 they are subjected would in time destroy them were they not continually grow- 

 ing, or being replaced by a pulpy secretion at their bases. The molars vary in 

 number from twelve in the upper, and ten in the lower, to but two in each jaw ; 

 these, like the incisors, are composed of two substances ; an external layer of 

 hard enamel, and a softer material in the interior ; their sui-faces are irregular 

 or tuberculated, adapted for grinding vegetable substances. These teeth are 

 replaced in the same manner as the incisors. 



The forms and habits of the animals in this order are of a great variety. They 

 will be discussed in the descriptions of the different fomilies, of which we have 

 in this country five. They constitute each a natural group, with generally fa- 

 miliar representatives. They are called the Sciuridfe, (the squirrels;) Sacco- 

 myidcE, (the pouched Yats and gophers;) Muridce, (rats and mice;) Hystricidce, 

 (porcupines ;) and Lcporid<x, (rabbits and hares.) The detailed peculiarities of 

 these families cannot be, in the present paper, discussed at great length, but 

 those most prominent will be mentioned sufficiently to have them understood. 



The Sciuridce of the United States are included in the two natural divisions 

 or sub-families Sciurnice, (squirrels and woodchucks;) and Castorin(B, (beavers.) 



The sub-family Sciurince, in which are placed the squirrels, both ground 

 and arboreal, the wood-chucks and spermophiles, is very numerous in this 

 country, and the members of it are generally injurious, from the ftict that the 

 great bulk of their food, of which they generally secure large quantities for 

 their winter subsistence, consists principally of the various seeds, nuts, and 

 grains which are valuable as a means of subsistence to man and the domestic 

 animals. These animals also consume great quantities of cultivated fruits, and 

 even vegetables, to an extent, in some districts, involving to the farmer con- 

 Biderable pecuniary loss. Wood-chucks, especially, are very mischievous, not 

 only in what they eat, but to the crops of clover, grass, and grains, which are 

 destroyed by numerous trails or paths leading from their burrows. This family 

 is of small value, either for food or for their fur. 



The Castorince, or beavers, are of no great importance, economically speak- 

 ing, to agriculture. They are valuable for their fur, which always commands 

 a ready sale at a high price. These animals are rapidly becoming extinct, and 

 are only found in the wildest and most retired districts of the" country. 



In the family Saccomyidce. are included all the gophers and pouched rats. 

 They may be readily distinguished by their large cheek pouches. These ani- 

 mals are all eminently injurious. They burrow in the earth in grain fields and 

 grass lands, and often do considerable mischief by visiting the gardens, orchards, 

 and nurseries, where they eat the roots of the plants and gnaw the bark from 

 the trees. In this manner large numbers of fruit trees are destroyed yearly. 

 The cheek pouches are used in conveying food to their burrows. This food 

 consists of roots, grains, gi-asses, seeds, fruits, and nuts. Of these they devour 

 great quantities. Various methods have been devised for their destruction, the 

 most successful being by poison. Great numbers are destroyed by the carni- 

 vorous animals and birds, and were it not for these they would, in consequence 

 of their numbers and rapid increase, be a serious pest. These are, however, 

 not found in New England. 



The great family MuridcB is, economically speaking, the most important in 

 our indigenous Rodentia. In it are included the rats and mice, all of which 

 are injurious, in some genera, seriously so. These animals have characteristics 

 in common, but they naturally fall into several groups, which possess peculiari- 

 ties sufficiently marked to rank them as sub-families. Tbey are called the 

 DipodincB, (jumping mice;) Murince, (rats and mice proper;) and Arvicolince, 

 (short-tailed field mice.)* 



