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THE LIVING WORLD. 
The Boomer, or Mountain Beaver (. Haplodon rufus ), is substantially 
tailless, lives inland, and burrows in the dry land. Its habitat is Oregon, 
Washington and California. It adds to our illustrations of the changes which 
animals undergo to adapt them to their environment. 
PORCUPINES, CAVIES, AGOUTIS, AND OTHER RODENTS. 
The two sub-families of the hystricidce , or porcupines , are the cercolabma 
and hystricina. The cercolabina is confined to America, and the latter is spread 
over the old world. In both sub-families, the collar bones are nearly perfect, 
attached to the sternum but not to the shoulder blade; the eye cavities are 
very large; the forehead very broad; the cheek bones destitute of an angular 
process on the lower margin ; the molars four in each side of the upper jaw, 
and four in each side of the lower jaw; the dorsal vertebrae usually fourteen, 
and the lumbar, four; the feet short, body more or less armed with spines or 
quills, capable of being raised by muscles under the skin. The cercolabma 
live almost entirely in trees, and their feet have generally only four equal toes 
with long compressed and curved claws; there are sometimes five toes on the 
hind feet; the soles are thickly studded with small flattened warts; the skull 
short and broad, with a minute lachrymal 
bone forming no part of the lachrymal canal; 
the palate between the molars is on a lower 
level than the anterior portion; the molars 
converge in front, and are distinctly rooted, 
each having a fold of enamel on either side, 
the worn crown presenting two deep transverse 
cavities surrounded by enamel; incisors small; 
anterior and posterior clinoid processes want¬ 
ing. This sub-family contains the genera 
erethizon , cercolabes and choetomys. The genus 
erethizon has a non-prehensile tail, short, thick, 
flattened, covered at the base above with 
hairs and spines, and on the under side and at the apex with stiff bristles; 
nostrils close together; feet short and broad; toes four or five, with long curved 
claws; hind feet with a distinct inner toe with claw, without any projecting 
semicircular lobe on the inner side; upper lip slightly notched, but with no 
naked mesial line; body stout and covered with a long and dense fur from 
which the spines project, limbs short-and strong. 
The Capybara ( Hydrochoerus capybara) abounds in South America; it is 
killed for its flesh, is persecuted in the water by the crocodile, and hunted upon 
land by the jaguar, so that it must often wonder whether life is worth living. 
It is about the size of a sheep, has a large mouse-like head, small, round 
ears, great black eyes, a nose set off with formidable whiskers, a short neck, 
short legs, a coarse covering of russet hair. When in motion it has the 
appearance of a prize hog, but when seated on its haunches it looks like 
nothing but itself. 
The Patagonian Cavy (. Dolichotis patagonica) is a burrowing animal, but 
sometimes takes possession of the excavations made by other creatures, instead 
of constructing its own home. It is found, sometimes, a long way from its 
retreat; two or three generally go together on these rambles. In its manner 
European hedgehog (Erinaceus europczus'). 
