At bar 67 Clementi uses the octave quavers, derived from the first subject, but in two-part counterpoint, often in contrary motion.
But... 6/8 Six eight The signature six-eight has six quavers or their equivalent in a measure.
Be aware - many players speed up when playing quavers.
But I can't remember whether Byrd gives 2 quavers and splits the word into its syllables on paper.
Although there are several quavers, the rhythm consists mostly of crotchets.