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.
In the more typical Lemuridae there are two pairs of upper incisor teeth, separated by a gap in the middle line; the premolars may be either two or three, but the molars, as in the lower jaw, are always three on each side.
Till recently the aye-aye was regarded as representing a family by itself - the Chiromyidae; but the discovery that it resembles the other lemurs of Madagascar in the structure of the inner ear, and thus differs from all other members of the group, has led to the conclusion that it is best classed as a subfamily (Chiromyidae) of the Lemuridae.
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.
Belonging to the family Lemuridae (see PRIMATES) it typifies the subfamily Indrisinae, which includes the avahi and the sifakas (q.v.).