Shape notes were a kind of musical notation used in 19th C American hymns where the shape of the notehead told one how far to jump (a third, a fifth, etc) to get to it. I've been told that once you master them, shape notes make it very easy to sing songs in parts.

Many shape-note collections end in 'harmony' for example, Southern Harmony, Missouri Harmony, Columbian Harmony. But the first (?) and best-loved was called The Sacred Harp.

I just played a beautiful melody, 'Prospect,' from that tradition in church yesterday.