Ichthyosaurus conybeari is a rare species, previously known only from an incomplete holotype and one referred specimen, both from the Lyme Regis area of the west Dorset coast, U. K. A newly recognized, nearly complete specimen (NMW 93.5G.2) is the first occurrence of the species in Somerset, U. K. A revised diagnosis recognizes new morphological characters that distinguish the species: slender maxilla with a long, delicate premaxillary process; narrow postorbital; humerus with an anteriorly offset dorsal process that has a well-defined lip extending slightly into the shaft; fibula that is much larger dorsoventrally and mediodistally than tibia; and wide rectangular ischium that is much shorter than the pubis and femur. Notching of anterior fin elements in the forefin had been used as a diagnostic character, but a review of notching within Ichthyosaurus suggests that it has little taxonomic utility. Another specimen (NHMUK R15907), herein referred to the species, extends the range of I. conybeari from the upper Hettangian to lower Pliensbachian stages of the Lower Jurassic, the longest duration of any species of the genus.