Though in no way related to squirrels, which belong to the rodent order, they may easily be mistaken for them at a distance. They are all of small size, and very similar, in their mode of climbing, to squirrels. Their nails, also, except those of the hind-thumbs, are long and claw-shaped; and the thumbs of the fore extremities, or hands, are not opposable to the other fingers. Their bodies are long and slender, clothed with soft hair; and their tails, though not prehensile, are nearly twice the length of their bodies. MIDAS URSULUS. The midas ursulus is found in the Lower Amazon, frequently in the neighbourhood of towns, and it seems much less afraid of man than most other monkeys. It is seldom that more than three or four individuals are seen together. It moves generally among the larger boughs and trunks of trees, its long nails assisting it to cling securely to the bark. It lives on both animal and vegetable food; the former including various insects, eggs, and occasionally a young bird--while its vegetable diet consists of all the sweetest fruits it can find. The smaller insects-- flies, and other soft-bodied creatures--it pops into its mouth whole; but when eating a larger one--such as a cockroach--it nips off the head, wings, and legs, before putting it into its mouth. It has gained the name of oustiti, in consequence of its giving vent to a little sharp whistle when alarmed or irritated; but it otherwise generally preserves silence. The midas ursulus is about nine inches long; and the tail measures fifteen inches. It is clothed in a thick, long fur, and has a reddish-brown streak down the middle of the back. It is often seen in the houses at Para, and when treated kindly becomes very tame and familiar. When, however, strangers approach it, its dark, watchful eyes, expressive of distrust, observe every movement which takes place. MIDAS LEONINAS, OR JACCHUS ROSALIA. Another species, the Midas leoninas, or Jacchus Rosalia, inhabits the Upper Amazon. It is only seven inches in length. It is so named on account of the long brown mane which hangs from the neck, and gives it very much the appearance of a diminutive lion. One of these little creatures, kept tame, became familiar with every one, and used to climb up the chairs, over their shoulders and heads, just as a squirrel does. Mr Bates relates that one he met with, having reached his shoulder, looked into his face, showing his little teeth, and chattering, as though it would say, "Well, and how do you do?" It exhibited more affection towards its master than to strangers, and would climb up to his head a dozen times in an hour, and make great show of searching for certain animalcule.