All the Malagasy lemurs, which agree in the structure of the internal ear, are now included in the family Lemuridae, confined to Madagascar and the Comoro Islands, which comprises the great majority of the group. The other families are the Nycticebidae, common to tropical Asia and Africa, and the Tarsiidae, restricted to the Malay countries.
The gentle lemurs (Hapalemur) have a rounder head, with smaller ears and a shorter muzzle, and also a bare patch covered with spines on the fore-arm.
The sportive lemurs (Lepidolemur) are smaller than the typical species of Lemur, and the adults generally lose their upper incisors.
Till recently the galagos have been included in the family Lemuridae; but this is restricted to the lemurs of Madagascar, and they are now classed with the lorises and pottos in the family Nycticebidae, of which they form the section Galaginae, characterized by the great elongation of the upper portion of the feet (tarsus) and the power of folding the large ears.
The main facts at the present day are, firstly, the restriction of the Prosimiae, or lemurs, to the warmer parts of the Old World, and their special abundance in Madagascar (where other Primates are wanting); and, secondly, the wide structural distinction between the monkeys of tropical America (Platyrrhina), and the Old World monkeys and apes, or Catarrhina.