Tetratonic scale

[4] Amongst the Arapaho, Blackfoot, Crow, Omaha, Kiowa, Pawnee, and Sioux, as well as some Plateau tribes, especially the Flathead, the tetratonic and pentatonic scales used are anhemitonic (that is, they do not include semitones).

[5] Tetratonic scales have also been noted among the music of the Creek Indians,[6] and in the Great Basin region among the Washo, Ute, Paiute, and Shoshone.

[11] On Guadalcanal in particular, anhemitonic pentatonic and tetratonic scales are the predominant types, although the minor second does nevertheless occasionally appear as a melodic interval.

[13] In eastern Uganda, the Gwere use for their six-string harp (called tongoli) a tetratonic scale in which all the intervals are nearly equal, which to Western ears sounds like a chain of minor thirds.

[16] The music of the Volga-Finnic Cheremis (Mari people) of central Russia was primarily pentatonic, but used tetratonic scales 20% of the time.