I am currently working on transcribing an old SATB score (circa 1920) and I came across a type of note for which I have no name. It is the same size as a grace note, but it has a full note value, is unconnected to either the tenor or bass parts (at least visually), and is the fifth of the chord (I have read that grace notes often provide leading tones for the main note). I am thoroughly confused by this and am stuck in researching it, mostly because I have no name for it. What is this called, and what does it musically represent?
The score may be seen at the Library of Congress. I agree with Lars Peter Schultz's suggestion that this is an optional divisi in the lower voices.
The fact that the note is smaller is what indicates that the note is optional. The upward-pointing stem does normally indicate that the note should be sung by the second tenors, but it would be more normal for it to be sung by the first basses, for considerations both of range and of voice leading. It might even make sense to divide the tenors and basses equally there, having 1/3 each of the basses and tenors sing the D. In practice, the decision would depend on the singers in the ensemble.
That there is nothing making this explicit is perhaps a bit puzzling, but you might also see it as an instruction from the arranger to do whatever works best for your group.
There are other optional alternate notes in the bass part, beginning with the last note of the next-to-last system, and continuing through the end of the following measure. These, however, are different, since they are below the regular-sized bass notes and share their stems with them. Still, the performers will have to decide whether it is an optional divisi or an optional lowering of the part by an octave.
There's also a bass divisi near the end of the verse, on the downbeat of the third measure at the top of the second page. In this instance, interestingly, none of the notes are smaller (despite the fact that the voice leading for the first bass is perhaps somewhat awkward).