Fuxian species

One of my recent referrals was a Google search for Fuxian species. I can help with that:

First Species: 1:1, all whole notes all the time. Only consonances are allowed (unisons, 3rds, 5ths, 6ths, octaves, and 10ths).
Second Species: 2:1, one voice is in half notes. Any dissonance must be a passing tone.
Third Species: 4:1, one voice is in quarter notes. Dissonances can be passing tones or neighboring tones.
Fourth Species: 2:1, sort of, really 1:1 but one voice is shifted by a half note, tied over the barline, until the cadence. All dissonances are suspensions.
Fifth Species: a mix of all the previous species, known as free counterpoint. This is the end result that is closest to actual 16th century music.

For more details, consult Gradus ad Parnassum.