236 U. S. P. R R. EXP. AND SURVEYS ZOOLOGY GENERAL RKPORT. 



does not appear to cross this river into Texas, except in the western part of the State; it extends 

 along the Rocky Mountain range certainly as far as 38 N., and west to the Pacific, where it 

 reaches nearly to the Columbia river. Perognathus, with similar limits on the whole is found 

 on the Missouri river as far east as Fort Union, Nebraska, though it is not known whether it 

 occurs in a direct line between this point and Matamoras, where it has been detected by Dr. 

 Berlandiere and Lieut. Couch. 1 Geomys has a more general distribution, being found in 

 Georgia and the Gulf States, and from the region bordering the Mississippi, to the Rocky Moun 

 tains, and even almost to the Arctic Sea on the north, and to Central America on the south. 

 All the pouched rats hitherto collected west of the Rocky Mountains, however, belong to the 

 section Thomomys, which is limited eastward by the Mississippi. 



Muridae. Of this, the most extensive family of the Rodents, the North American represen 

 tatives are not very numerous, being confined principally to the Arvicolinae. The Dipodinae are 

 illustrated by the genus Jaculus, with one or two species, most abundant in the northern part 

 of the continent, and extending to the Pacific. The Ctenodoctylinae are confined to Africa. Of 

 the Murina we have no Old World Mus; our few species of mice belonging to the American 

 group of Hesperomys, which, in a small number of species, is found all over the continent to a 

 very high latitude. It is in South America that the Hesperomys, in several subdivisions, reach 

 their highest development, eighty or more species being enumerated. Of Reithrodon, distin 

 guished from Hesperomys by the grooved upper incisor, and likewise found in South America, 

 there are only a few North American species, belonging to the southern States and the Rocky 

 Mountains. The Neotoma, with thin tails, are found in the southern States, and through Texas 

 and northern Mexico perhaps southern California to the Pacific ; more sparingly in the 

 western States. A few specimens of N. floridana have been caught by Mr. John G. Bell near 

 the city of New York, far out of their usual range. The bush-tailed Neotomas occur on the 

 head waters of the Missouri and west to the Pacific ocean, probably also in California; their 

 extreme northern range has not yet been ascertained. An extinct species, N. magister, Baird, 

 much larger than any of those now existing, was formerly very abundant in Pennsylvania, as 

 shown by numerous remains found in the bone caves about Carlisle, Harrisburg, and other 

 localities. Sigmodon has much the same southern and southwestern distribution as Neotoma, 

 though there is as yet no evidence of its occurrrence west of the Rocky Mountains. 



Of the remaining sections of Muridae, viz: Spalacinae, Bathyerginae, find Arvicolinae, the 

 latter alone occurs in North America, where it is very fully represented by the genus Arvicola, 

 with numerous species spread all over the continent. Here also belong Myodes, confined mainly 

 to the Arctic circle, and Fiber, distributed as widely as Arvicola. The two first mentioned 

 genera are found in Europe, but not at all in South America, nor scarcely in Mexico ; the last 

 is found only in North America. 



Hystricidae. Of this family, North America possesses but one genus, Eretliizon, of a single 

 sub-family, Hystricinae, and probably but a single species, or at most two ; of upwards of eighty 

 species enumerated in the family, but four are found in the Old World, the rest being South 

 American, with the single northern exception just stated. Among the South American Hystri 

 cidae there is found the largest of living Rodents, the Capybara, though this, in turn, is much 

 exceeded in size by the extinct Castoroides, represented in North America by C. ohioensis. 



Leporidae. The numerous species of hares belonging to the genus Lepus may be said to 

 characterize North America above all other countries, twelve or more being enumerated. They 



1 Since this was written a itpecics lias been detected at Fort Riley, Kansas. 



