Having thought about this awhile, it seems to me that the last two lines ("Resolutio") explain the first two mensural lines. The "1 (over) 2", "1 (over) 3", and "1 (over) 4" are mensural indications that basically say a semibreve gets multiplies by 2, 3, and 4, respectively, as evidenced in the resolution (the semibreve of the upper two lines becoming a breve, dotted breve, and a long, respectively). The clef seems to be a Fa clef. This is supposedly a canon, but I'm not sure what the delay and pitch of the second voice is ... possibly a fourth above (or fifth below)?

I don't see any obvious indications that it's a canon showing multiple voices from the single part; at least that's not apparent from the notation. Is there any other information?

What we do have in the image is one melody set out twice. In the upper two staves, it is shown using proportion signs. The proportions show various levels of augmentation, as CHGiffen suggests. In the lower two stave it's shown again but without any of the proportion. In other words, the augmentation is all written out.

The clef looks like a soprano clef (bottom line is middle C).

Hope that helps!

Although others would surely prefer something like one of these ;)

Patrick, thanks for the notation!

So I got it from a collection called "Compendium Musicae," late 16th century, editor was Adam Gumpelzhaimer. It seems to be anonymous...and now I'm questioning if it's even a canon.

Relevant pages in the collection (large file) are PDF pages 31 ... and maybe 32: https://vmirror.imslp.org/files/imglnks/usimg/9/9a/IMSLP292132-PMLP325522-gumpelzhaimer_compendium_musicae_1591_386871701.pdf

Any more insight is so welcome! I've very intrigued by this...