 The existence of a "pyknon" therefore depends on the uppermost interval being larger than half of a perfect fourth, which occurs only in the chromatic and enharmonic genera.Because the diatonic genus consists of two whole tones and one semitone, no single interval is larger than the other two combined, and so there is no "pyknon" .For this reason, the enharmonic and chromatic genera are sometimes called the "pyknic genera", in order to distinguish them from the diatonic .