You've got that right. Guy stopped by the store yesterday, wants to sell me a low-grade (and incomplete) rod-bayonet rifle, "you know the square one". When informed that there were two choices, round and triangular, he said (a bit put off at being corrected) that it was the latter. I showed him a picture of mine and he said "yeah, that's it, but I don't think it has those" (pointing to the grooved finger pieces at the rear of the latch).
Hmmm - IF he is right (and the odds are VERY slim indeed) then it is POSSIBLE that he MIGHT have one of the impossibly rare 28" M1882 short rifles, since they are the spitting image of the M1880, save for lacking the thumbpieces!
Stay tuned - all sorts of things could go wrong with this wet dream.