I think that's an over-braider foot. Braid fed through non scoop end to be sewed to material (that foot is over).
With my National "Viking" art deco newly arrived, I am learning that the National/Eldridge sewing machine co. had a colorful corporate history, with machines under many, many labels. Some were made by National and labeled by others; a few may have been made by others and labeled as Nationals.