Californian Prong-gilled Mayfly (Paraleptophlebia californica)
This species was described in 1934.
The Californian Prong-gilled Mayfly was endemic to California, USA, where it was originally found in the Waddell Creek in Santa Cruz County. It was subsequently (in 1968) found near the Anderson Fork, a stream north of the city of Chico in Butte County.
The species was never found since and is considered most likely extinct.
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edited: 31.10.2017