FIGURE 3. Conceptual model showing the non-planar orientation of a single Phycosiphon burrow lobe with the mantle and spreite shown as being transparent to facilitate viewing of the central mudstone strand. 3.1. Lobe parallel to the bedding plane; 3.2-3.3. Possible variations of twisted Phycosiphon burrow lobes. This model is an expanded version of the bedding plane conceptual model (Bromley 1996), but incorporating the possible twisting allowed by the emended diagnosis of Wetzel and Bromley (1994).