FAMILY. 
HYSTRICID AE. 
Molar teeth, ; muffle, or terminal portion of the muzzle, clothed -with small hairs; the skull with a large ante- 
orbital opening through which a portion of the masseter muscle passes as well as the infra-orbital nerve. Lower jaw with 
the angular portion joined to the outer (not the under) surface of the bony covering of the inferior incisors. Tibia and 
fibula distinct. 1 
The family of Eystricidae, of which the porcupine is a well known example, is almost entirely 
American, and in fact chiefly confined to the southern portion of the continent, where most of 
the species of Rodents belong to it. The only Old World species belong to the genera Eystrix, 
Aulacodus, and Petromys. North America possesses hut one genus, Erethizon, hut Mexico, in 
addition, has Cercolabes, and perhaps some of the South American types may he found on its 
southern borders. A few species occur in the West Indies, of which Capromys fournieri is the 
most remarkable. 
The family Eystricidae , embracing as it does so great a variety of different forms, cannot be 
so sharply defined as that of Leporidae with its two genera. Very great diversity of opinion 
has in fact existed as to the arrangement of the genera, many of which have been widely sepa¬ 
rated from their allies in a natural system of classification. By uniting those having the 
features given at the head of the article, it will he found that the forms most closely allied in 
reality are brought together, and an equal degree of harmony is established in the geographical 
distribution of the species. 
The Eystricidae , as arranged by Waterhouse, are divisible into six sub-families, viz : Eystri- 
cinae, Dasyproctinae, Echimyinae, Octodontinae, Chinchillinae, and Caviinae ; of these, only one, 
viz., Eystricinae, is represented in the United States by species of Erethizon, erroneously referred 
by most American authors to Eystrix, a genius of a different division of the sub-family. Mexico, 
however, has an additional genus, Cercolabes, belonging to the same division. 
The chief characteristics of the six sub-families of Eystricidae, according to Waterhouse, are 
as follows : 
I. Caviinae.— Molars rootless, divided by folds of enamel so as to form lobes having acute angles ; the series of molars 
on opposite sides of the upper jaw converging and nearly meeting in front; incisor teeth comparatively short, those of 
the lower jaw not being extended backwards as far as the springing of the angular portion or descending ramus. Four 
toes to the fore feet, and three to the hind. Tail wanting, or rudimentary. Upper lip entire. A strongly developed hori¬ 
zontal ridge on the outer surface of the lower jaw ; the angular portion of this jaw produced much beyond the condyloid 
portion, descending below the level of the dentary portion, and with a curved lower margin. Clavicles wanting. 
The principal genera of this family are Dolichotis, Cavia, and Eydrochoerus, the latter, in¬ 
cluding the Capybara, or Capinche, the largest of living Rodents. 
II. Chinchillinae. —Molars rootless, with parallel or nearly parallel transverse plates of enamel; the series of molars on 
either side of each jaw converging in front. Tail long, or of moderate length, recurved and bushy. Clavicles perfect, 
slender. Fibula very slender. Hind feet with less than five toes. 
1 Waterhouse. Nat. Hist. Mamm. II, 1848, 147. 
