We have restudied some of the material of a fossil anostracan originally discussed and illustrated by Palmer from the Middle Miocene, Barstow Formation, near Yermo, California, and we now recognize it as a new species, Branchinecta barstowensis. It is the best-preserved fossil anostracan known to date. The closest affinities of this species are with B. pollicifera Harding, 1940, collected from the mountains of Peru and Bolivia around Lake Titicaca.