Protomycena is an extinct monotypic genus of gilled fungus in the family Mycenaceae, of order Agaricales. At present it contains the single species Protomycena electra, known from a single specimen collected in an amber mine in the Cordillera Septentrional area of the Dominican Republic. The fruit body of the fungus has a convex cap that is 5 mm (0.2 in) in diameter, with distantly spaced gills on the underside. The curved stipe is smooth and cylindrical, measuring 0.75 mm (0.030 in) thick by 10 mm (0.39 in) long, and lacks a ring. It resembles extant species of the genus Mycena. Protomycena is one of only five known agaric fungus species known in the fossil record and the second to be described from Dominican amber.

The Agaricales are an order of fungi in the division Basidiomycota. As originally conceived, the order contained all the agarics, but subsequent research has shown that not all agarics are closely related and some belong in other orders, such as the Russulales and Boletales. Conversely, DNA research has also shown that many non-agarics, including some of the clavarioid fungi and gasteroid fungi belong within the Agaricales. The order has 46 extant families, more than 400 genera, and over 25,000 described species, along with six extinct genera known only from the fossil record. Species in the Agaricales range from the familiar Agaricus bisporus and the deadly Amanita virosa to the coral-like Clavaria zollingeri and bracket-like Fistulina hepatica.