Charles, thank you...seems to be a tough case to crack!

Here's an attempt. The rhythm at fidelium is very tricky. It looks the same as amoris, but the longer note value before the syncopation really makes it challenging.

Heath might have given a little context: what is this from?

Ok. Thanks for that context, Heath. I think my initial guess was right, and that it's not a two-from-one canon. Rather it's a music example showing the use of proportion signs for augmentation. Here is a translation of that paragraph:

Now then there follow the proportions of augmentation, of course, the sub-duple, sub-triple, and sub-quadruple. These then can all be comprehended under one rule, that within each proportion, all the notes and rests are augmented by whatever time the numerator is contained in the denominator, in the following manner: in sub-duple, everything is doubled; in sub-triple, everything is tripled; and in sub-quadruple, everything is quadrupled.

The music example shows an example of each of these proportions in the first two lines, and in the second two lines it is shown written without proportion signs. Such late examples of proportion are always deliberately weird theory exercises, meant to show the power of the notation; these are not things you would ever encounter in a piece. The best way to read these numbers, as Tinctoris suggests, is to think "[numerator] in the time of the [denominator]." Thus the first proportion (1/2) is "one semibreve in the time of two semibreves." In other words, you have to double everything. In actual practical music from the sixteenth century, the only proportion sign you are likely to encounter is cut-c 3/2, which means roughly that the breve gets the tactus and that you sing three semibreves in the time of two. Of course, in actual performance, what this means for tempo is by no means a settled question without controversy! Is it tactus-equals-tactus, bar-equals-bar, minim-equals-minim, or just do whatever you want?

Patrick, while I do think your second effort is more prayerful, of course, I do want to ask why you chose four-to-one reduction, which I think makes this more confusing. In other words, you take the semibreve of the regular, non-augmented version, as the quarter note. This makes it seem odder than it really is. I'd prefer to see a notation like what Gumpelzhaimer shows in lines three and four.