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 ; Habrothria, an Arvicoline group, with a short and thinly haired 
tail; and Oxymycterus, 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! 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 Rhipidomys, 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 Cricefus are abundant in the Pleistocene cavern- 
deposits of Brazil, where a number 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? (Nectomys).—The Rats of this genus are allied to 
the American forms of Cricetus, 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® 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. 
Lhithrodon,* and Ochetodon2—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.6—A peculiar North American genus, in which the 
teeth simulate the prismatic appearance of those of the _4rvicoline. 
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 
Baris tale + Proc. Zool. Soc. 1884, p. 451. 
* Brandt, Mém. Acad. Imp. St. Pétersbourg, sér. 8, vol. iii. p. 428 (1835). 
* Say and Ord, Journ. cad. Philad. vol. iv. p. 352 (1825). 
+ Waterhouse, Proc. Zool. Soc. 1837, p. 29. 
° Coues, Proc. Acad. Philad. 1874, p. 184. 
6 Say and Ord, Journ. Acad. Philad vol iv, p. 846 (1825). 
