274 MAMMALS. 



wise have been described as new, turned out to be mere varieties of one or other of the Common 

 European Rats ; for instance, a Rat from Maldonada, near the mouth of the La Plata, which had 

 sufficiently distinctive characters to lead to its being described and named (Mus maueus), examined 

 with this light is only a dark variety of the Brown Rat. Mus Jacobin, from the GalajDagos, is 

 another variety; and an isolated species, Mus Islandicus, found nowhere but in Ascension Island, 

 is only the Common Black Rat slightly modified. 



A higher rank or degree of organisation has been inferred to belong to the Old-world Rats 

 than to the New, from the former usually extirpating the latter, when they come in contact ; but the 

 facts will hardly bear out this inference, for not only is the suj)eriority due simj)ly to the greater size 

 and more powerful teeth of the conquering species (chiefly the Brown Rat), but it is exercised by 

 them as much upon their own countrymen, the Old-world species, as upon the New. 



New-World Rats and Mice (Sigmodontes). The old name, Mus, has been reserved for the 

 Old-world species. There are several appellatives for the New-world groups. Some of these (the 

 genera Hesperomys and the North- American Reithrodons) are small and mouse-like ; others 

 (HoLOCHiLUs and Neotoma) are rat-like ; and Sigmodon is like the Arvicola, or Field-mouse. 



Cotton Rats (Sigmodon). There are only two species of this genus. They are about the size 

 of the Norway Rats, and look Kke ArvicoLjE. They are confined to the southern portion of the 

 United States, from Carolina westwards to Western Texas. 



Bush and Wood Rats (Neotoma). These are there presentatives of the larger Murid.^ in 

 North America. Some have scaly tails, like our Rats ; others have the tail bushy and furry, like the 

 Dormouse, and the fur soft and full. Some of the species are very large, greatly exceeding the 

 Brown Rat in size, and they are also much superior to it in beaut}^ and docility. The genus 

 is confined to North America, and occurs throughout the greater j)art of it. It is, however, not 

 found in the New-England states. It is met with from the Missouri to the Pacific, and from 

 Mexico northwards. The fossil remains of one extinct species have been found in the caves of 

 Pennsylvania. 



Vesper Mice (Hesperomys). The range of this genus is very erroneously laid down in most 

 Physical Atlases— Johnston's and Berghaus' among the rest. It is found over the whole of the 

 continents, both of North and South America ; but the South American species all differ a little from 

 the North American ; and not only so, but none of the sub-sections into which they have been divided 

 are found in botli. Three out of several sub-genera, originally suggested by Waterhouse, have been 

 adopted for the South American species ; and Baird has made three more for the North American. 

 The differences on which they are founded are, however, all slight in degree, and do not correspond 

 with any geographical limits, the species being mingled with each other, except that the South 

 American sub-genera, taken as a body, are slightly different in type from the North American, and 

 are for the most part larger in size. Allowing for exceptions in both countries, they can be best 

 characterized by saying that the South American species are all Rats, and the North American all 

 Mice, there being only one North American species of any size, and it not exceeding the dimensions 

 of a half-grown Norway Rat. Dr. Baird says, "A striking feature of the North- American 

 Vesper Mice, to anglicize Wagner's name, is their diminutive size compared with the South 

 American. Many species of the latter are fuUy equal to the Rats, or even larger, some of them, 

 as Holochilus, with still larger teeth. Scarcely one of our " (North American) " species exceeds 

 four inches to the root of the tail in the flesh, while most are the size of the Common House 



