(Greek: "through tones", "diatonic")
The genus with two whole tones and a semitone, or any genus in which no interval is greater than one half of the fourth.
By "one half of the fourth", Chalmers means the irrational interval size 4/3(1/2) = ~1.154700538 = ~249.0224996 cents, which is the maximum possible size of a pyknon.
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