556 U. Ss P. R. R. EXP -AND SURVEYS—ZOOLOGY---GENERAL REPORT. 
The species of this sub-family inhabit the mountain regions of Chile and Peru, one only 
occurring in the plains of La Plata: They belong to the genera Lagostomus, Lagidium, and 
Chinchilla ; the latter embracing the species which furnish the valuable fur called chinchilla. 
III. Ocropontrvaz.—Molars rootless, with but a single indenting fold of enamel oa cither side, or rarely with an extra 
fold on the inner side of tho molars of the lower jaw. Zygomatic arch, with an angular process on the lower edge. Hind 
feet with five toes ; fore feet likewise with five toes, sometimes only four. 
This family is readily distinguished from the other sub-families with rootless molars, Caviinae 
and Chinchillinae, by the possession of five well developed toes on the hind foot; the presence of 
a distinct tail separates it from the Cavies, while the short hairs of the same member prevent it 
from being confounded with the Chinchillas. The genera Habrocoma, Octodon, Schizodon, 
Spalacopus, and Ctenomys, are all confined to the middle and southern regions of South America, 
occurring on both sides of the Andes. Most are of small size, and some present quite a close 
resemblance to forms of other families. Thus Ctenomys, with its short tail, enormous incisors, 
broad depressed body, small ears, and very long fossorial claws, resembles Geomys most remark- 
ably, except in wanting the external cheek pouches. 
TV. Ecumryryar.—Molar teeth complicated and (with one or two exceptions) rooted. Malar bone with a distinct angular 
process on the lower edge. Both fore and hind feet with five toes. 
The genera of this sub-family are Capromys, Plagiodonta, Myopotamus, Cercomys, Petromys, 
Dactylomys, Loncheres, Mesomys, Echimys, and Aulacodus, These are confined to South America 
and the West Indies, excepting Petromys and Aulacodus, which are African. The species are 
more numerous in this than in any other sub-family of Hystricidae. 
V. Dasyproctinar.—Molars semi-rooted and arranged in parallel series. Cranium elongated; nasal bones rather short 
and broad; malar bones destitute of a descending process on the lower edge. A tolerably distinct post-orbital process 
formed chiefly by the frontal bone, but in part likewise by the squamosal. Scapula, with the emargination in the fore part 
of the spine, but moderately deep. Clavicles wanting. Feet formed for running, with the toes 5—3 or 5—5, terminated 
by sub-solid nails, which are but little arched. Tail rudimentary. Body clothed with hair only, no admixture of spines. 
The two genera, Coelogenys and Dasyprocta are inhabitants of South America, ranging as far 
south as Paraguay and Bolivia, occurring also in some of the West India islands. The genus 
Osteopera of Harlan was founded by him on a skull picked up on the banks of the Delaware, 
and erroneously supposed to have floated down from the interior of Pennsylvania, where it 
existed as a native. It has, however, proved to belong to a Paca, Coelogenys paca, which had 
probably died in some menagerie and been thrown into the river. 
VI. Hysrriomvar.—Molars rooted or semi-rooted. Skull with the malar bone destitute of angular process on the lower 
margin. Frontal bones very broad. Feet short; the toes 5—5, 4—5, or 44. Body more or less armed with spines. 
The species of the group as thus defined are found in both the Old and New World. Water- 
house, however, is inclined, with Brandt, to establish two main divisions of the porcupines, 
and even to raise them to the rank of independent sub-families. These may then bear the 
names of Hystricinae proper, and Cercolabinae; the former confined to the Old World, the 
latter to the New. The characteristics of these sections are as follows, beginning with the 
Philogaeae, or 
Hystricinae.—Consisting of porcupines which live on the ground and seek shelter in burrows 
which they themselves form. They have five toes to both the fore and hind feet. The soles 
are naked and smooth. The upper lip is divided by a vertical groove which runs up to join a 
transverse fissure which unites the nostril openings. The skull is more or less elongated and 
