166 RODENTS. 
the greater part of their length form star-like spots among the dark fur. These 
bristles and the spines on the back are black at the tips. 
This species inhabits the forests on the eastern coasts of Mexico. Nothing 
special is recorded of its habits; but it may be mentioned that from observations 
made on captive individuals of other species, it is probable that none of the tree- 
poreupines ever drink. It is stated that in those long-haired species in which the 
fur is of a greyish tint, the general appearance of the animal when reposing on the 
arm of a tree closely simulates a gnarled and lichen-clad knot. 

MEXICAN TREE-PORCUPINE (4 nat. size). 
Thin-Spined A peculiar porcupine (Chatonys subsprnosus), from Central and 
Porcupine. Northern Brazil, differs from all the members of the preceding genus 
by the shape of its skull and the more complicated structure of its molar teeth, as 
well as by the slenderness of its spines, which may be described as half-way 
between those of the other groups and mere bristles. It is a large species, of a dull 
brown colour, with the under-parts inclining to rufous, and the feet and tail 
brownish black. The tail, although long, is not prehensile ; and the habits of the 
animal are less completely arboreal than those of the preceding group. Remains 
of a species of Hrethizon occur in the superficial deposits of Pennsylvania, and those 
of Synetheres in the caverns of Brazil. 
With the true porcupines, as typically represented by the 
common South European species (Hystria cristata), we come to 
the second subfamily, all the members of which are confined to the Old World, 
and differ from their Transatlantic cousins by the following characteristics. 
Externally the soles of the feet are perfectly smooth, the fore-feet have a small 
thumb, and the female is provided with six teats. In the skeleton, the collar- 
bones are incomplete; and the molar teeth have imperfect roots. In habits all 
True Porcupines. 
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