Reticulomedusa greenei
Pennsylvanian
Francis Creek Shale
Pit 11, Will Co.
Illinois, USA.

Classic example of this rare jellyfish. Other interpretations have suggested it might even be a variation of preservation of the anenome Esssexella showing the tentacles. As with all Mazon Creek fossils, the strange impressional preservation keeps scientists busy.

100mm in 100mm half-concretion