Rob Parsons kindly shared these images with me. I’m sure many of you will have seen this pen before, in slightly different configurations and with different names.
It isn’t quite a fountain pen, in that it needs frequent intervention by the user to keep the ink flowing. It’s more of a dip pen with a reservoir.
Sometimes this pen appeared with its own fountain pen style nib, others, like this one enable the fitting of dip nibs.
An interesting sideline to fountain pen history.