This is a W.F. Tubbs "Sno-Shu" folding canoe chair/seat. They are from the early 1900s, originally from Norway, ME (company founded there in 1907), then later from Wallingford, VT. They made snowshoes also, and like their snowshoes, these are made of steam-bent ash with woven rawhide. The chairs/seats came with multiple "leg" configurations. Yours appears to be one of the shorter models. They can be used in the floor of the canoe, or shorter ones might be sat up on the existing canoe seat but with any height at all, this could make the canoe unstable. They were also used as camp chairs, doing double duty when taken on a canoe trip.
Here is a photo of a Tubbs brass tag to compliment the one Benson posted below:
And here is another form of Tubbs marking - a simple stamp in the same general location: