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the Oriental Region and Tachyoryctes in the Ethiopian Region.
The Pocket-gophers (Geomyidm), which are entirely restricted to the Nearctic Region, contain only two genera and nine species. Allied to them are the Heteromyidm, a more numerous group of seventy or eighty species, entirely restricted to the New World, and, with the exception of a few stray species of Pocket-mice (Heteromys), to the Nearctic Region.
The tenth family of Rodents, the Bathyergidm, belong entirely to the Ethiopian Region, over which they are thinly represented by fifteen or sixteen species. The Naked Sand-Rat of Southern Abyssinia and Somaliland (Hcterocephalus glaber), is one of the most extraordinary-looking Mammals in the world, being almost entirely without hair and covered with a yellowish naked skin; it is subterranean in its habits.
The Dipodidm, or Jerboas, which we now come to, are well known for the great length of the hind limbs and the kangaroo-like manner of their progression; they consist of six genera and about thirty-three species, all of which, except one (Zapus), are restricted to the Palsearctic Region. The six species of Zapus, are spread over the Nearctic Region from the far North down to Mexico, where, however, they are restricted to the highlands.
Allied to the Jerboas is the Jumping-Hare (Pedetes coffer), which forms an allied family of itself, and is restricted to Southern and South-eastern Africa.
We now arrive at the series of Porcupiny Rodents, of which as many as seven families are usually recognized. These are mostly found in the Neotropical Region,
and four of them indeed, the Chinchillidm, Dasyproctidm,
Dinomyidm, and Caviidm, containing what are usually called the Chinchillas, Agoutis, Giant-mice, and Cavies, are entirely restricted within its limits, while a fifth family, the Erethizontidm, or Tree-Porcupines, has a single genus in the Nearctic Region.
The Octodontidm, a large group of seventy or eighty species, divided into some twenty-two genera, are also mostly Neotropical, but four peculiar types, Ctenodactylus, Massoutiera, Pectinator, and Petromys forming a little group by themselves, are Ethiopian. The true Porcupines, Hystricidm, of which three genera are known, are found in the Ethiopian, Oriental, and Palaearctic Regions, typical Hystrix being the only one met with in Europe and Northern Asia.
Finally, at the close of the long series of Rodents, we have the two groups of Pikas and Hares, markedly differing from the nineteen previous families in their dentition, and therefore assigned to a separate Sub-order of Rodents as Duplicidentati. The Pikas (Ochotoma), of which some sixteen species are recognized, are restricted to the highlands of the Nearctic and Palsearctic Regions. The Hares (Leporidm) have a much wider distribution, having representatives in every part of the world's surface except in the Australian Region and Madagascar. Of Lepus proper some sixty species are now recognized, the greater number of which occur in the Palaearctic and Nearctic Regions, whilst they are generally scarcer further south, though well represented in Africa
Section V.—Summary And Deductions
Table of genera of Rodents, showing the geographical distribution of the species.