In the case of the Octave the species is distinguished on the Enharmonic scale by the place of the tone which separates the tetrachords, the so-called Disjunctive Tone ([Greek: tonos diazeuktikos]). Thus in the octave from Hypatê Hypatôn to Paramesê (_b-b_) this tone (_a-b_) is the highest interval; in the next octave, from Parhypatê Hypatôn to Tritê Diezeugmenôn (_c-c_), it is the second highest; and so on. These octaves, or species of the Octave, the writer goes on to tell us, were anciently called by the same names as the seven oldest Keys, as follows: Mixo-lydian _b - b_ 1/4 1/4 2 1/4 1/4 2 1 Lydian _b*- b*_ 1/4 2 1/4 1/4 2 1 1/4 Phrygian _c - c_ 2 1/4 1/4 2 1 1/4 1/4 Dorian _e - e_ 1/4 1/4 2 1 1/4 1/4 2 Hypo-lydian _e*- e*_ 1/4 2 1 1/4 1/4 2 1/4 Hypo-phrygian _f - f_ 2 1 1/4 1/4 2 1/4 1/4 Hypo-dorian _a - a_ 1 1/4 1/4 2 1/4 1/4 2 On the Diatonic scale, according to the same writer, the species of an Octave is distinguished by the places of the two semitones. Thus in the first species, _b-b_, the semitones are the first and fourth intervals (_b-c_ and _e-f_): in the second, _c-c_, they are the third and the seventh, and so on. He does not however say, as he does in the case of the Enharmonic scale, that these species were known by the names of the Keys. This statement is first made by Gaudentius (p. 20 Meib.), a writer of unknown date. If we adopt it provisionally, the species of the Diatonic octave will be as follows: [Mixo-lydian] _b - b_ 1/2 1 1 1/2 1 1 1 [Lydian] _c - c_ 1 1 1/2 1 1 1 1/2 [Phrygian] _d - d_ 1 1/2 1 1 1 1/2 1 [Dorian] _e - e_ 1/2 1 1 1 1/2 1 1 [Hypo-lydian] _f - f_ 1 1 1 1/2 1 1 1/2 [Hypo-phrygian] _g - g_ 1 1 1/2 1 1 1/2 1 [Hypo-dorian] _a - a_ 1 1/2 1 1 1/2 1 1 § 24. _Relation of the Species to the Keys._