Temnodontosaurus platyodon, from the English lower Liassic (Hettangian and Sinemurian), is a large ichthyosaur that reached an estimated length of almost 9 m (29 ft). Although represented by at least 13 specimens, few are complete, and the species cannot be described as well known. A similarly sized species from the upper Liassic (Toarcian) of Germany has hitherto been referred to a separate genus, but is shown here to be referable to Temnodontosaurus. This species, T. burgundiae, shares several features in common with T. platyodon, including a small orbit, modestly sized teeth, a relatively long maxilla, forefins probably with four or less digits, notching in at least some of the elements of the first digit, a distally expanded humerus, and a discrete pubis and ischium. An emended diagnosis is given for Temnodontosaurus. Poorly known giants from the English lower Liassic, represented only by isolated teeth and girdle elements, may have reached lengths of 15 m (49 ft). This at least equals the size of the largest known ichthyosaur, Shonisaurus. These mysticete-sized reptiles may have fed upon other ichthyosaurs.