New specimens of the Kimmeridgian cryptoclidid plesiosauroid Kimmerosaurus langhami Brown provide additional data on the morphology and ontogeny of the skull, and the anterior cervical vertebrae are newly described. An emended diagnosis is given and the possibility of the synonymy of Kimmerosaurus with the 'elasmosaur' Colymbosaurus, the only other British Kimmeridgian plesiosauroid, is considered.