The bulbus type is just a round cap without any gills. It was first seen in Constantine's Manor, one hidden in each of the enormous trees (one is at the bottom of a hollow tree, from which there is no way out, the other is at the end of a hole in the base of the second tree), and again in the subterranean caverns next to a large boulder near Raoul. This type is seen more in Thief II: The Metal Age, particularly in "Trail of Blood" mission. It cannot be picked up, as it disappears when touched. It was evidently meant to burst into a cloud of smoke in imitation of a real puffball, but this does not occur because the slay result in DromEd was set to "Destroy". This can be amended by changing the effect to "Normal" for each of these mushrooms.
It is possible that Burricks eat glowing mushrooms, as these are always present in their tunnels.