_Lemuroidea._ The Lemurs are small, monkey-like quadrupeds. They are mostly nocturnal, arboreal creatures of comparatively low organization. The body is furry. The orbital and temporal fossæ freely communicate. The lachrymal foramen is situated outside the orbital fossa. The dentition of the Lemurs varies greatly; in some of them it is 2/2 1/1 3/3 3/3 for both jaws. In nearly all of them the median incisors of the upper jaw are separated by a median space. Both feet have flat nails on all the digits, except the second of the hind-foot, which has a claw. The thumb (pollex) and the big toe (hallux) are well developed. The cerebral hemispheres are only slightly convoluted, and do not entirely overlap the cerebellum. The transverse colon is almost always folded on itself. There may be a pair of teats on the abdomen. The uterus is two-horned, and the placenta is diffuse. This sub-order comprises the Lemurs proper (_Tarsius_, _Lemur_, and other genera) and the Aye-Ayes (_Chiromys_). _Anthropoidea._ The Anthropoidea are the most highly organized Primates. They are chiefly modified for an arboreal life. The body is hairy instead of furry, but only slightly so in man. The incisors do not exceed 2/2; the molars are 3/3, except in the marmosets, where they are 2/2. The upper, median incisors are in close contact. The orbital and temporal fossæ are separated by a broad vertical plate. The lachrymal foramen is situated inside the orbital fossa. All of the digits are provided with flat nails, except in the Hapalidæ, in which all except the big toe (hallux) are provided with a claw. In some the thumb (pollex) is rudimentary or absent. The clavicle is well developed. The cerebrum is usually richly convoluted, and more or less completely covers the cerebellum. The uterus has no horns. The placenta is deciduate and metadiscoidal. The Anthropoidea are subdivided into the two following groups: Super-family 1.—_Platyrrhinæ_ (New-World Monkeys). Super-family 2.—_Catarrhinæ_ (Old-World Monkeys). The Platyrrhinæ or New-World Monkeys are subdivided into the following families, viz.: Family 1.—_Hapalidæ._ Family 2.—_Cebidæ._ The Catarrhinæ or Old-World Monkeys are subdivided into the following families, viz.: Family 1.—_Cercopithecidæ._ Family 2.—_Simiidæ._ Family 3.—_Hominidæ._ _Hapalidæ._ The Hapalidæ or Marmosets are no larger than squirrels, being the smallest monkeys. They are found mostly in Brazil.