Riedelia[2]) is a genus of diatoms known from the fossil record, comprising approximately three species.

Many of the species were originally described under the closely allied genus Hemiaulus.

Paleontologists Hans-Joachim Schrader and Juliane Fenner, working with fossil specimens obtained from Leg 38 of the Deep Sea Drilling Program in the Norwegian and Greenland Seas, decided that several previous descriptions of diatoms belonging to Hemiaulus were rightfully placed on Williamriedelia.

Schrader and Fenner note that while Hemiaulus diatoms have polygonal areolated valves, Williamriedelia valves are punctate with isolated punctae.

[3] Riedelia clavigera is known from fossils dating from the early Eocene to the middle Oligocene.