The remaining genera of Vole-like Murines are Phenacomys and Synaptomys from North America, and Siphneus from Palaearctic Asia. Evotomys is one of those genera which are common to both the Palaearctic and the Nearctic regions, but the bulk of the species are North American.
Sub-Fam. 9. Sigmodontinae.—This is the name given to another sub-family of Murine Rodents, a group which includes the Hamsters in the Old World as well as a large number of South American genera of Rat-like animals. Of these latter there are a very large number, the bulk of the group being American.
The Hamsters, genus Cricetus, as it is usually called, although apparently the correct name is Hamster, are Old-World forms of Pouched Rats. The Common Hamster, C. frumentarius, is about 210 mm. long, with a tail of 58 mm. It has cheek pouches. The small and the large intestines are not very unequal in length, and the caecum is fairly large, being about one-sixth to one-seventh of the length of either. It is a purely vegetable-feeding creature, and in Germany where it occurs (and from which language its vernacular name is derived), hibernates during the winter in its burrow, having previously surrounded itself with a great accumulation of food carried thither.
To North America are peculiar the genera Onychomys, Sigmodon, and Peromyscus. The genus Sigmodon, the Cotton Rats, reaches Central America, and even gets a little farther south. The other two genera, though mainly North American, also extend their range to the south. Onychomys has hairy
foot-pads, a state of affairs which characterises a number of these Rodents.
The genera Megalomys, Chilomys, Reithrodontomys, Eligmodontia, Nectomys, Rhipidomys, Tylomys, Holochilus, Reithrodon, Phyllotis, Scapteromys, Acodon, Oxymycterus, Ichthyomys, Blarinomys, Notiomys are South American forms. Oryzomys and Rheithrodontomys are common to both parts of the New World.
The genus Ichthyomys is remarkable on account of its un-Rodent-like habits and of certain associated structural changes. I. stolzmanni was obtained from Mount Chanchamays in Peru at an altitude of 3000 feet; it is a habitual fish-eater, and lives in streams. Another species, I. hydrobates, was formerly referred to Habrothrix. The skull shows likenesses to that of the Australian Hydromys; but the most marked characters of adaptation are those of the teeth and caecum. The cutting edges of the upper incisors form a reversed
of obvious use in holding a slippery fish. The caecum is much reduced, short, and narrow. The general Otter-like shape of the creature is largely due to its flattened head, though its "size and general proportions are much as in the common Black Rat."[[336]]
This sub-family contains a number of genera from Madagascar, viz. Brachytarsomys, Nesomys, Hallomys, Brachyuromys, Hypogeomys, Gymnuromys, and Eliurus.