Hi all, Its good when your questions spur me to check up on facts, helps to improve and sharpen the old brain!!
Here's a new septarian nodule pic
As you see there are 2 kinds, brown, more irregular shaped and full of a crazy paving of crystal filled fragments, and the type of my first post, ie the grey cushion type and 1 broken piece to show the calcite filled interior.
The ammo fossils are on the exterior surface (not in this photo though)
I looked up my source Arkell "Geology of....Weymouth, Swanage, Corfe and Lulworth" 1968 reprint
He definitely calls these structures septarian nodules. SO unless there is a more up-to-date definition these are septaria!! Further along the foreshore are another type, still round, grey, but like a pad of bulbs which are stuck together with calcite, and fall apart very easily.
Do enlighten me if I've got it wrong!!! Heath