Cryptosaurus (meaning "hidden lizard") is a dubious genus of dinosaur known from a partial femur from the Late Jurassic of England. The femur was found by the geologist Lucas Ewbank and donated by him to the Woodwardian Museum at Cambridge in 1869. Cryptosaurus was the same year named by British paleontologist Harry Seeley; the type species is Cryptosaurus eumerus. The genus name is derived from Greek kryptos, "hidden", a reference to the rarity of the find.