Nice find. The "Tauchpanzer Maus" is priceless.

Actually, that is not a variant design or such, but the standard planned procedure for crossing waterways with the Maus... as awkward as the Maus design concept was in itself, at least they were sensible enough to expect NOT finding bridges capable of shouldering the Maus´ 180 tons.
Thus, river crossing was to be done by using an electric motor powered by cable link from another Maus which waited on the riverbank, then would cross itself. The air tunnel would be used to supply air to the crew (although I find the use of the term "schnorkel" suspect in this case).