464 RODENTIA 



short and Hamster-like, and the form is Arvicoline ; Scapteromys, of 

 Murine form with a long and hairy tail ; Phyllotis, with a shorter 

 tail ; Habrothrix, an Arvicoline group, with a short and thinly haired 

 tail ; and Oxymydems, distinguished from the preceding by having 

 a nail instead of a claw on the pollex. With regard to the dis- 

 tribution of these forms Mr. Thomas 1 remarks that in South 

 America as we proceed southwards there is a general tendency " to 

 a disappearance of the tropical and northern Mouse- and Dormouse- 

 like subgenera Ehipidomys, Vesperimus, and Oryzomys, with the 

 appearance and increase of the Vole- and Hamster-like Habrothrix 

 and Calomys a change that is curiously paralleled in the Old World 

 by the gradual supercession of Mus and Myoxus in favour of Arvicola, 

 and Cricetus as we go northwards from tropical to temperate and 

 arctic regions." One species has spines in the fur. 



Remains of Cncetus are abundant in the Pleistocene cavern- 

 deposits of Brazil, where a numbel of the forms are referable to 

 existing species ; the genus is also represented in the Miocene of 

 North America and Europe, the species from the former area having 

 been described as Eomys, and those from the latter as Cricetodon. 



Holochilus 2 (Nedomys). The Rats of this genus are allied to 

 the American forms of Cncetus, but have the third upper molars 

 proportionately larger and the skull more stoutly built. This 

 genus is confined to Brazil, and contains about six species, some of 

 which are the largest indigenous Rats of America. Two species are 

 aquatic in their habits, and have short webs between the toes of 

 their hind feet. 



Sigmodon 3 differs from Cricetus in the pattern of the molar 

 teeth. It contains one species only, the Rice -Rat, S. hispidus, 

 ranging from the United States to Ecuador. 



Rhithrodonf and Ochetodon. 5 These are more or less like 

 Cricetus, but with grooved upper incisors. The first is a South- 

 American genus, and contains five Rat - like species, one from 

 Venezuela, another from Peru, and the other three from Patagonia. 

 The second consists of three North American mice, of about the 

 size and proportions of the English Wood-Mouse (Mus sylvaticus). 



Neotoma? A peculiar North American genus, in which the 

 teeth simulate the prismatic appearance of those of the Arvicolince. 

 There are four species known as Wood-Rats, all of about the size 

 of Mus decumanus ; one of them (N. cinerea) having a tail almost as 

 bushy as a Squirrel's while the other three have ordinary scaly 



Rat-like tails. 



1 Proc. Zool. Soe. 1884, p. 451. 



2 Brandt, Mtm. Acad. Imp. St. Pttersbourg, ser. 3, vol. iii. p. 428 (1835). 



3 Say and Ord, Journ. Acad. Philad. vol. iv. p. 352 (1825). 



4 Waterhouse, Proc. Zool. Soc. 1837, p. 29. 



8 Coues, Proc. Acad. Philad. 1874, p. 184. 



6 Say and Ord, Journ. Acad. Philad vol iv. p. 346 (1825). 



