Reticulomedusa
Reticulomedusa is an extinct genus of prehistoric cnidarian containing a single species, Reticulomedusa greenei. It is known from the Mazon Creek located in Illinois. Although it was once described as jellyfish, it may be pedal or oral disc of Essexella which is reinterpreted as sea anemone. References 

Fossil taxa described in 1979
Prehistoric cnidarian genera
Carboniferous cnidarians
Fossils of the United States