Hery A. Lauer (1983): Archäologische Wanderungen - Nördliches Niedersachsen, Westliche Lüneburger Heide, Mittelwesergebiet: Ein Führer zu Sehenswürdigkeiten der Ur- und Frühgeschichte, S. 100
The Wikipedia article also speaks of a rare form of a trapezoidal passage grave. Unfortunately, I still do not have the Sprockhoff Atlas (even used it is too expensive), so I cannot say what he wrote about it :(
Something is not right. This message is just to keep things from messing up down the road